The amount of Steam bashing and unadulterated ignorance flying around on these forums sometimes is simply ridiculous.. people are freaking out over Steam? It uses all of 20mb of system RAM to stay open, jees.
You can even disable almost all of it's features and go bare bones down to 15mb of system RAM. You can right click a friend and instantly join their game, this is only a good thing for Civ.
Why do you want to sell Steam to us?
The issues people have with Steam go far beyond just how much memory it uses in the background. For example, many don't appreciate the fact that the license to play civ5 will now simply be a "subscriber agreement" and if you, say, do something against Steam's terms of service in another game on your account, there is potential to ban you from playing civ5. One of the things included in the reasons for closing someone's account is negatively affecting the enjoyment of Steam by other subscribers.
While I find Steam to be bearable (I use it for a couple of games, mainly TF2 - a game where for obvious reasons it's fair enough to be Steam exclusive), I also find it introduces a bunch of complications that are nothing to worry about at the best of times and damn nuisances at the worst of times. For example, it is difficult to install steam games to different partitions. It is possible using hardlinks I'm told but for many users this is too advanced. Then again, the users for who that is too advanced are probably the same users who don't have more than one partition.
Steam takes time before it launches a game. With civ4 I play PBEM games so I load up the game intermittently sometimes, preferring to use windows explorer to manage my files rather than in game. With civ5 I wouldn't be surprised if ALT-tab now gets broken and to avoid having to restart the game over and over, with steam's delay, we would have to do everything from inside the game. I find civ4 loads very quickly when I launch it by opening a save from windows explorer.
Things like that are just simpler when there isn't an extra layer between you and game (e.g. Steam). To me, the selling points of Steam e.g. friends lists and achievenments

lol

at the moment are outweighed by the likely inconveniences we will suffer at times. I don't believe I need to "bash" steam for what it does, but I equally don't see why I have to be perfectly happy about it either.
You can right click a friend and instantly join their game, this is only a good thing for Civ.

I can appreciate you like this feature about games that use Steam, but I'm not sure it will even be all that important for civ5. We don't even know yet whether it will be possible or recommended to "join" an existing game, whether a friend is in there or not. We can only assume at this time that civ5 is not like TF2 where you can jump right into an existing game and do it often. In civ4 multiplayer, it was usually a nuisance when a player joined an existing game (usually because it would sometimes cause game to hang, at other times because we wanted the original player to rejoin).
And to the above post, the Steam UI update was the first mandatory Steam update in I believe three years. You can turn off your game updates too, or download them elsewhere away from Steam and install them manually if you REALLY don't want Steam on the internet.
If the bolded part has been confirmed for civ5 please provide a link. IIRC someone asked this question of 2K Greg and I'm expecting a reply when he finishes the FAQ.