I just dinged 80 the other day and i quested to get there. I'm now doing the low level dungeons in northrend and i have a question. When i'm tanking a boss am i suppose to gather up the adds as well or leave them to my dps?
In most cases, yes you do need to deal with them. There are a few exceptions.
UK : 1st and 2nd bosses have adds, in both cases they are your responsibility.
UP : 1st boss, the adds aren't tankable, everyone just needs to DPS them down. 3rd boss, they stop spawning when you get the boss. You still need to hold any that are still up.
AN : 1st boss - unless you screw up or are going for the achievement, all adds are dead before the boss. 2nd boss, same thing. 3rd boss, adds alternate with boss. Worry about the big ones, the little ones die too fast to wory about tanking.
OK : 1st boss, only the Guardian add do you really need to worry about.
Nexus : General, all adds are your responsibility. Anomolus, with a well geared group you can largely ignore the adds, with low gear you need to deal with them. Crystalus, not really your problem.
Occ : all adds are your issue
Drak : 1st boss, ignore them. 2nd boss, during first phase, the ones one the ground are yours, and the DPS should be able to deal with everything from the stairs w/o you. 3rd boss - all yours.
Gundrak : Only adds are on the snake, and you can't really do much about them.
HoS : Brann is all adds and they are all your issue. Last fight it depends on the groups gear level. Overgeared groups you can ignore them, low gear, you need to pick them up.
HoL : General - your responsibility. Rock dude - they randomly retarget fairly often and aren't tankable.
ToC - The ghouls during black knight randomly retarget and are only semi-tankable.
FoS - no adds on bosses
PoS - 1st boss, they are yours to hold onto.
HoR - the 'adds' such as they are are really the whole fights in question and are yours to deal with.
What Theotherone said is generally true, however try not to get in the habit of ignoring adds. I made this mistake last night. I was tanking H UP last night and on Skadi (3rd boss), apparently 2 more adds spawned after he landed and I missed them. Nuked my healer and wiped . Situational awareness is key for a tank. You should always be ready to pick up adds at any time.