The Slow and Meticulous Dungeon Runner...
Let's say that you're trying to get a weapon from Heroic Trial of the Champion, a set of legs from Heroic Utgarde Pinnacle, and a belt from Heroic Nexus. That's all you need. You just want to run those three instances. You can do this, but you can't do it with any of the perks of doing a random dungeon.
Just hit that little drop-down in the upper right hand corner of your Dungeon Finder frame. It's the one between the quest and the role icons. Select 'Specific Dungeons' from the dropdown and you'll get a list of all of the dungeons available to you.
Uncheck the box next to the headings of each group and then only check the dungeons or heroics you really really need.
Once you're done, just hit 'Find Group' at the bottom and everything will proceed from there like the random dungeons do. The only difference is that you won't get any rewards from doing it this way other than those things that drop in the dungeon. No extra badges, no bags of goodies, no extra gold.
However, since most people will be hitting the random dungeons you'll be able to find a group much faster. The program behind the scenes just picks one of your specific dungeons and grabs 4 people wanting to do random dungeons and tosses you all into a group together. Yes, that means even if you want something from Oculus, you'll still be able to find a group.
Let's set some ground rules...
The first rule of the Dungeon Finder is that it does not work on raids.
The second rule of the Dungeon Finder is that it does not work on raids.
Blizzard added a new interface for joining raids. The Dungeon Finder helps you find parties for dungeons using everyone in your battlegroup regardless of server. Being as raids are still going to be same-server only, that means you won't be using this tool for it. Plus there's the fact that you can't use this tool for it. Raids have their own new interface that's very similar to the specific dungeon interface. See the Raid panel of your Social window for more info on that.
The old Looking for Group channel now has nothing to do with the Dungeon Finder. Looking for Group is now just a channel like trade available in all major cities. That means anyone who is currently spamming trade with group information can now do that on a channel actually designed for it.
You can choose to queue for one of the following at a time, but no more than that: dungeons, battlegrounds, arenas. Pick your queue of choice and commit to it. If you want to queue for a dungeon, get done with that and then queue for an arena or battleground afterward, that's perfectly fine. You just can't queue for Halls of Lightning and Alterac Valley at the same time.
Need before Greed is the law of the land. Blizzard put the random dungeon loot requirement as need before greed in order to help prevent as many loot disputes as possible. If you don't want to use that for your loot distribution, then you'll have to create your own group by hand. Sorry.
Disenchanting is now a type of roll, but only if you have an appropriately leveled enchanter in your party. This is considered a greed roll. If you happen to win, the game automatically shards the item and puts the resulting mats in your inventory. This might rub a lot of enchanters the wrong way, because of long standing traditions on their servers, but there's not much you can do about it. The good news is that this should help reduce the price of enchants on the market as more mats should start being available.
The randomness of the random dungeon dailies aren't completely random. While the text does specify the dailies as random, they're not really. The system tries to make sure you aren't running the same dungeon over and over again. With random mode on, it will allow you to bypass your normal heroic lockouts. This means if the dice gods are against you, that random dungeon could be one you really don't like. However, the system tries really hard not to do that.
If you're choosing specific dungeons through the interface, it will still take your heroic lockouts into account, so you can't just choose to run new Icecrown heroics over and over again. Now, if you've selected random dungeons and everyone else has selected the new dungeons specifically, like on oh, I don't know... patch day. You might be able to get the new dungeons over and over again. But that's just luck if it happens and don't count on it.
Gallery: Patch 3.3: Dungeon Finder Guide
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.