are pullups a good mass builder for biceps and upper back?

yes, very good upper body movement

Yes.

Depends on HOW exactly it is that you do them though.

Different techniques can work different parts of your body.

sweet...Pullups is the exercise I'm best at...what is the difference between the under hand, and the overhand grip?

Overhand incorporates your lats, while underhand is basically your biceps.

Lei, you're partially right; underhand will incorporate more of your biceps but both will include your lats.

a bunch of different variations in the middle of this article

http://www.bodybuilding.com/fun/charles4.htm

I havent done pullups for a week, and just got done doing them...wow...my arms feel like balloons. My abs even kill because my feet were raised slightly in the air when doing them...I did 3 sets..one of 5, 3 and 2. 10 seconds up and 10 down....I like it.

When I do my pull ups I try to go fairly slow, but not 10 seconds up and down...maybe 5 up and 5 down..I usually go very fair grip, as fair as possible actually and bend my legs and cross them to prevent swaying..I go for as many as possible per set then jump softly off the gruond and do a couple more...I also read somewhere if you bring the back of your neck up to the bar inetad of trying for your chin over the bar it will incorporate the lats much more...great for v shape..

you mean bringing the bar behind your head? ive heard that thats not a good thing to do, easier to get hurt or something