Sorry for the delayed responses. Had to step away to attend to some business, but i'm back.
Stalin006 & Cjtheman316,
ok now ..........waht about nuclear weapons? should u use them? and waht if the AI uses them on u, and what if the enemy (it will be more easier to hapend on PTW against someone else) sees ur invasion troops and sends in a nuke? all ur forces are killed in a second!, also sometimes otehr civs allie w/ ur enemy and end up w/a 3 front war......mmmh.......any answers?
As mentioned before in this thread, be careful with Nukes. Nukes have extreme public relations impact and can quickly change the course of a war, or even the game. Even allies you've nurtured for thousands of years can turn on you if you abuse nuclear warfare. Also, there are environmental considerations with the random changing of topology after the launching of nukes (although the effects and reparcussions are not as drastic as real life).
My humble advise is broken into 2 phases: pre- and post- Satellites. Satellites is the technology that allows the creation of ICBM, the most deadly and convenient form of nuclear warfare. You can launch an ICBM at any city or tile in the game without need of transportation. Just aim and fire. If you or other Civs have this technology and therefore, the ability to potentially build ICBMs, then exercise the greatest caution in using ICBMs. I wouldn't say to not use them because they can be very devastating, especially when aiming at enemy capitals and their other largest and most productive Civs. First of all, many city improvements and garrisoned units will potentially be destroyed. IN many cases, the city population will be cut in half! The surrounding city tiles will instantly be poluted and all roads and railroads destroyed. So, in one turn, you've decimated an enemy's city. It may take them 100 years to rebuild that city, which is a major hit.
However, as mentioned before, you have to consider the counter attack. Sometimes, the entire world will suddenly declare war against you. If other Civs can potentially build ICBMs, then the counter attack can reap the same damages on yourself as well!
Post-Satellite Considerations
I'd take the following tips into consideration before using a single ICBM:
1. Military Strength. How strong are you? Do you have the production might and infrastructure to take on the world? Do you have the most superior naval and air force than your competitors? This will mean that you can whether the storm and defend against attacks at home and in lands you've conquered.
2. Resource Dependence. Do you currently trade for key strategic or happiness resources? If you do, I wouldn't do it, especially if you're using either a Republic or Democratic gov't. If your trading buddy declares war with you, losing those resources may cripple you. Further, if you're not a Civ with the Religious trait (like Egypt, my favorite), then switching governments will cripple you even further. Don't forget, in the Modern era, your cities are large and more mature, which means that Anarchy is a true nightmare!
3. Workers Out of Work. Usually by the time you're waging Modern Era wars, you'll have a ton of workers "out of work". A handful of workers will be on duty cleaning up polluted squares, but the rest will be twidling their thumbs fortified on some square waiting for the employment market to bounce back (especially after 9/11 and the recession we're..... oops, we're talking Civ not real life. Sorry, I digress

). This is important because, let's say a counter attack nuke gets through the cracks and hits one of your cities. Having these workers is key to getting a city's surrounding infrastructure back together and even adding workers back to the city's population to make it grow again. (IN the rare occassion where i've had a counter attack nuke land, I was able to get the city back up and running in about 3 turns!)
3. Nuclear Defense. How strong is your military defense? Being that we're talking about post-satellite, have you discovered "Integrated Defense" and built the Strategic Missile Defense small wonder? Do you have SAM Missile Battery improvements built in all key cities?
If you pretty much meet the above conditions, give or take, then give it a go! I've had a game where I built around 20 ICBMs (I had a monster city with Iron Works, Factory, Mfg Plant, Solar Plant spitting them out in like 3-4 turns!). Once I used the second ICBM everyone declared war on me! Well, needless to say, everyone got a little "ICBM" tough love from me! I launched every one of them on the most powerful of the other civ's biggest cities. Through espionage, I caught a couple of ICBMs in production and sabotaged them a turn before they were built! It was then excited by the Fourth of July display that happened next. I watched as my Nuclear defense system kicked in as 5 ICBMs were short out of the sky! That was cool

to see. Anyway, that's that.
Pre-Satellite Considerations
Pre-Satellite is a little different and easier to manage. Your nuclear weapon is the Tactical Nuke, available with the discovery of Space Flight. The nuke must be
phycially delivered via Nuclear Submarine and even then, Tactical Nukes have a pretty limited range (6).
Usually, i've found that using carefully orchestrated Nuclear Warfare using Tactical Nukes can be usefull and fun! Several have mentioned the Capital City isolation strategy and have thoroughly explained its virtues (Thanks, Catt!

), but I find it much more fun to implement this strategy with a good Ol' T Nuke! Get the same results in one turn!
As for the back lash, it is much easier to manage before Satellite is discovered. You just have to have a defense in place that can look out for approaching enemy Nuclear Subs (see my post on "The Impenetrable Defense" coming soon....). The strength of your naval force should determine the likelihood of something sneaking through the cracks. I try to keep several Nuclear Subs patrolling the Coast and seas near my home continent to make sure noone is trying to get through, and Battleships are always at the ready to blow subs, battleships and transports out of the water.
In all, nuclear warfare is cool and such a rush! But exercise caution in your use. The above should be a start to a guide in considering if and when to use it.
DaDoo,
well if you got great leaders to waste...
rush a palace in that huge city you capture...
I don't think anybody ever got a city with palace flip.. right?
not practical at all but hey
Regarding having a city with palace flip.... No. However, its been proven that a city has flipped even when its had the FP! Sucks major. Coracle was happy for a week bashing Civ III after someone verified this.
Stalin006,
As for your point about a PTW opponent using a Nuke on you when you land.... that's interesting. I'd have to look into it further, but we all know different strategies will have to be employed when playing against human opponents (again, my thread "The Impenetrable Defense" is best suited for PTW games, or very persistent AIs). I can't imagine a player landing enough troops for me to even consider bombing my own country. The psychology of it is even crazy, even if you could quickly rebuild the tiles they landed on. I personally always build plenty of Artillery/Radar Artillery and Cruise Missile and keep them home so that, in case someone gets through my naval/air defense, they are still doomed. Then my super stack of MAs or Tanks always mops up what's left.
Remember, I said that I usually prefer to land my troops on a tile that's adjacent to a city, or I don't do it. That's with the Head of the Tiger. This way, the Artillery I bring along and any other 1 MP units can attack on the next turn. If I land, the opponent (AI, or human) will also have to consider the damage it will do to its own city. So, its not that cut and dry. I can see plenty of cases for and against. What do you all think of that?