Mastery and PvP

[:1]A rl friend and I are gonna roll in some 5's eventually (him being the hunter of course) and we're wondering if there's any point in a MM hunter getting a decent amount of Mastery. An extra arrow here and there seems kinda meh but I'm not an experienced hunter =) Any thoughts/suggestions?

Just sayin, he's VERY good, I know hunters aren't THE BEST in pvp currently but he knows how to pvp on a hunter very well (we were just under 2K in 3's and 5's in wotlk without much serious effort)
Mastery is more for constant dmg output, and is better if he can sit there and get off auto shots and other shots quickly.

Crit buffs all shots, and pet dps, and is said to be better for bursting someone down.

Imo crit is better for things like arenas... Mastery is godly for MM hunters though, but it goes off of all shots, and seeing as hunters have to basically be on the move 90% of the time, I think it will help a little bit more to reforge to crit.

However, if he is going to reforge to crit, I would say that he shouldn't reforge mastery into crit, just stats like haste, and hit.

(this is more just my personal flavor than anything else)