Underhand Bench press...

[Overload]

The pump you get is just because it's a different movement and your bi's are working to help support the weight. i get this from dips when i haven't done them in a while. i don't think it directly works you bi's but you biceps help support the weight in that movement(and most others) so in a sense they are getting worked by supporting the weight.


 

[Biggrnyou]

light weight close grip underhand presses are decent for triceps, but not sure the advantage over regular grips...

[Beyond Genetics]

They are great for Tri's but you have to put your thumbs on the same side of the bar as your fingers or it will twist your wrists....

Here's a guy doing it with 600lbs with ease and no bench shirt.

http://www.irongame.com/videos/20021117/AnthonyClark-ExhibitionLift-595RAWBP.ram

[BigAlski]

Well Anthony Clark is a special story when talking of reverse grip benches.  As I remember correctly, he benched 600 at HS age (probably 18-19) and wanted to be the first man to bench 600 reverse grip, either at any age or at some age, which I don't remember.  So anyways, he switched his grip and started training reverse but his training got ahead of himself and he couldn't really "revert" to normal grip because of his genetics and frame.  As he went heavier and heavier bearing the wieght could only be done reverse without a major setback so he kept it as such.  IIRC he benched reverse from then on.