Jealous?
Nah, I am genetically predisposed to a low body fat percentage. At my skinniest point, I had a six-pack, since then, I have gained 30 pounds and still have a six-pack.
Hogwash. They're an indicator of doing lots of ab-work. You can be skinny as a rail & not have them (I didn't). Likewise you can be heavier & still have them if you train them enough.
You can also be skinny as a rail, with minimal ab strength, and still have them. If your body fat percentage is over 14% or so, you can have any amount of ab strength, but you will not be able to see definition through the fat.
Genetics as to your body type have a lot to do with how visible your abs are at different levels of body fat as well, same people can have relatively low body fat and strong abs, but still do not have much ab definition.
I like them, k? Doing 20 pushups with 40 extra pounds on your torso is a lot harder than without. I've never worn a weight "belt" but it seems it would make one more prone to injury with all that weight concentrated around the lower-back area. Also, how do you bend with a heavy belt on?
Yes, they are good for pushups. I do pushups with a plate balanced on my back, which is a bit of a hassle. I would be wary of running with them though, that is a lot of extra stress, particularly on the knees, and I can think of better knee exercises.
By weight belt, I mean a belt you hang plates off of. There is really no extra stress on the lower back when wearing a weight belt. And you do not bend with a weight belt on.
Since you seem to be an expert of somekind though, what are "most important body weight exercises"?
I said that somewhat glibly, pushups are great, pullups and chinups are some of my favorite exercises of any kind. I really like body weight exercises for ab work. (crunches, reverse crunches, body levers, in that order of difficulty). Dips, and weighted dips are also excellent, you do need a certain amount of flexibility for them though. Handstand pushups are a fun challenge to work towards. (among a lot of other cool stand, flags and stuff)