I ran a PUG in Blood Furnace - Heroic last night. We ran it with a druid tank, pally healer, rogue, shaman, and a mage (me). When you enter an instance on heroic setting, you can bet that a lot of the mobs do a ton of damage. Most mobs would hit me for about 5k damage. Two hits, and I'd be dead for sure. With sap and sheep, most of the groups became fairly simple. None of the bosses gave us problems, but there were two areas that really gave us issues.
The first problem was in the room where the Maker is, IIRC. There's a patrolling group of 3 mobs. We just couldn't get one of them sapped, so that left us with 2 mobs to deal with. The druid that also has a high-end rogue said that he sapped them all the time, but after a number of failed attempts, we had to figure out alternate strategies. What we ended up doing was have one mob sheeped, one mob tanked by the druid, and then one mob evasion tanked by the rogue. Kinda risky, but it worked... mostly. The sheep was a little too close to the group in the center. I went to re-sheep him after the first guy died, but before the second died. Unfortunately, he resisted, and pulled that other group, which caused a wipe. Next time in, it was only 1 patrolling mob, so the rest of that room went smoothly.
The second problem came from the hall just before the last boss, Keli'dan the Breaker. There's a bunch of groups (probably 4) that have 2 Felguards. Some of the groups have a warlock with them as well, but with a mage, the warlock is no problem. Obviously with other classes (hunter ice trap, warlock banish), it would have been a piece of cake. The Felguards just hit for a ton of damage. And two on our one tank was just too much to bear. (Get it? Bear tank - bare. *cough* sorry.) After a few failed attempts to just burn the first one down, we were somewhat successful to have the rogue kite one while we killed the other. Unfortunately, a stealthed, respawned rogue killed our rogue and the Felguard came back. We killed one Felguard, but the other caused the wipe. We were down to 1 Felguard instead of two after we did the corpse run, but we'd kinda had enough. Luckily, the druid had a warlock friend that was nice enough to help us with those few pulls. Even then it was tough. At one point, with two healers, one warlock sheeped, and one Felguard banished, the second Felguard got off a shot that killed our tank. We chain banished and sheeped the mobs until he could run back.
I ended up getting a Primal Nether out of the deal, but it was really late. Was it worth it? Let me see how much I can get for a Spellstrike Hood and this Nether, and I'll let you know. heh. But seriously though, I was mainly wanting to get Honor Hold reputation for the Blade of the Archmage; the Nether was just a good bonus.