i have a prot pally (tbc), dk, and now warrior tank for my mixed-class group. all my accounts are cancelled until 3.3 for now, but it took me about 2 weeks to "gear up" my warrior. Warriors are DEFINITELY harder to multibox tank than pallys (easiest/best) or DKs, but once you struggle through and get the gear its not bad at all. I solo tank toc25, ony25, and even did a togc10 to anub this week on my warrior and he's been 80 for under a month. I'd say warriors are the most fun tanks since there just are a lot of things you can press while still feeling powerful, pallys are just sooo boring - consecrate and AFK.

A huge huge huge thing is simply gear, until you reach a good level of dodge/parry/block warriors take really big, big hits. I wiped sooooo much in heroic toc until my warrior was around 545 def, 36k hp, and 40%+ dodge/block/parry. After that it became easy.

this is my tank spam macro, I never have to really do much except spam it:

#showtooltip
/castsequence reset=combat/target Devastate, Devastate, Devastate, Devastate, Devastate, Shield Slam, Rend, Heroic Strike
/startattack

I do use devastate and sunder armor glyphs, forgot what the 3d is (shield block or shield wall?). its not a perfect macro, and I manually have to click revenge when it procs, and of course I manually shock wave early on. haven't had huge threat issues though when 5 boxing or solo and my guys are geared well.

Being an engineer is a HUUUGE help for a warrior tank, since I can rocket blast + heroic throw at the beginning of every boss pull for a nice 5k chunk of threat.