I run several sets of 3x hunters & 1 shammy (alliance & horde on one server and an alliance set on another server).

Even as a 4 boxer - I can handle most instances alone just 2-3 levels above normal. Smoked through Deadmines, Stocks, SM, Uldaman and Marudon (great lvl 50 quest bow there) in Azeroth instances - was leveling so fast from RAF bonus that a couple fo runs & the quests would get me a couple levels. Did Ramps and BF at 63-64. Zangamarsh at 65-66. Farmed Consortium rep in Auchidon at 68-70. At 72-73 was doing Slabs easily and Heroic Zangamarsh instances at 75. I do take care to enchant up & have food & potions & scrolls when I run a new one.

My main Hunter team dinged 80 a few weeks back and I had been running 3x BM with Gorilladins to level all the way. At 80 after 3.1 I switched to one BM main tank, one MM for trueshot and one SV for replinshment/traps. Still have all three pets as gorillas - like the interupt ability. Works ok - macros were a little fussy. Not clear to me that it is really better than 3x BM. Still gearing my guys up - so haven't tried any Northrend instances (beyond UK & Nexxus) alone yet.

http://www.wemultibox.com/blogs/singpraise for a little more info (I sux at blogging - sry)

Sing