I'd like to point out that to everyone saying that you need dps/heals, this is not true. No one is equal in the dungeon. As a tank I out dps all our our dps just about every pull, they may do a little more on a boss(not usually). I as a tank take no damage in heroics, and any damage taken I can easily heal myself before the next pull.
This is the exact reason I run with friends / guildies usually. They can toss me a heal if the healer is retarded and keep going without me having to stop and heal myself. This is a especially big deal at low levels, healer's don't know what they are doing and just dps away while your dying and then it's just 'oops'.