A feral in a group will usually be a tank, though we can dps quite well. But since dps is a dime a dozen and tanks are rare (and we have no indoors cc other than hibernate) we usually tank. Cat does do far superior damage than a bear but the bear can take a sustained pounding like no other class in the game. And bear is key for soloing sometimes too -- that's how you can solo elites and group quests.
If you go boomkin I imagine you will largely be expected to heal. I don't play boomkin but the 64 balance druid I grouped with last night said it was her first time ever where she was allowed to DPS. In all prior instances she was asked to heal.
There used to be a good druid tanking guide on this site, but I can't find anything in the newfangled wikicentric layout. If you've never tanked before, the basic principle is to keep the mobs' hate through a combination of damage and high aggro moves. At 58, your highest aggro move is mangle. By far. You can basically tank by serially mangling a mob and using maul if mangle is on cd and you have rage to spare (you burn rage by mauling; mangle and other instant attacks enable you to get some rage back from the damage you inflict). If you have to keep the aggro of multiple mobs, demoralizing roar and swipe will help. Make sure you position mobs so you don't break cc when you do this.
Bear tanking is pretty simple. Spam mangle with lacerate in there once you gain the ability at 66. Pull with feral faerie fire or cast spells if you feel fancy. Throw in roars if you have rage to spare and use fff liberally since it's rage free and builds a small amount of hate. Hit frenzied regen if you're in trouble and your healer is overwhelmed, bash casters or runners to stun them, and use feral charge to intercept mobs that break away from you and go for your teammates. There's a thread just below about the joys and pains of tanking; it's probably the toughest role in the game but exhilarating if you do it right.
If you end up dpsing, the cat's job is to stay behind mobs and shred. Mangle often enough to keep the debuff up to increase your shred damage and rip when you have adequate combo points. Don't waste a feral bite or maim unless the mob is almost dead. Our aggro dumping move (cower) is lousy, so be careful about building aggro, especially on bosses. But also remember, you're a hybrid. If the healer is down or cc'd, go caster and start healing. If the group is about to wipe, barkskin/tranquility. If the tank drops, go bear. If the healer drops, battle rez and innervate.
Edit: Sorry for wall of text but I read your post on main forum and understand better where you're coming from. You should make very clear to everyone when you tank if you haven't run the instance before and get full instructions from the vets, especially for the bosses. Also, another thing to remember as a tank is that you basically have to hit every mob that isn't cc'd. Why? Because every mob thats not glued to you will probably run to the healer. So it's best to concentrate your firepower on one mob (usually marked with skull icon and often the most dangerous in the pack) but to tab over and hit, maybe mangle, all other stray mobs to ensure they stay on you when your healer starts throwing heals. If the mob is trapped/sheeped/sapped you obviously don't have to do that -- in fact, if you hit it it will break cc and make your life worse. You should also keep an eye on cc'd mobs because when cc breaks they will attack whoever cc'd them. Sometimes this is no biggie -- a mage is supposed to keep his/her sheep sheeped and will simply resheep one that breaks. But a rogue can only sap out of combat, for example. So once that sapped mob wakes up, you need to corral it.
Edited, Jun 19th 2008 4:48pm by tuskerdu