Over on the European forums the developers posted some information about the new heroic system and the new daily quests coming in the new patch. Check out all the details about this new tool that should make finding groups easier on everyone.

Will the random heroic search have the option of excluding certain Heroic instances?
The dungeon finder will not let you exclude a specific instance, however - if you have already run a specific dungeon it is much less likely that the random heroic search will place you in the same dungeon again (on the same day).

Will players still need to purchase keys to queue for TBC heroics?
The tool complies with all standard requirements for entering a heroic dungeon. For example, if you log into the game right after 3.3 is released and queue for a random heroic dungeon, you will not be placed in instances such as Icecrown Citadel - Pit of Saron or Halls of Reflection unless you have cleared all the pre-requisites (previous wings in those cases) to unlock said instance entering (i.e. you must still clear Forge of Souls to enter Pit of Saron, and Pit of Saron to enter Halls of Reflection).

Is it true that players will no longer be saved to heroics? Does this mean players can chain farm heroics for Champion's Seals?
The Heroic lockouts still exist, however the difference is that the random heroic option will ignore any potential lockouts a player might have. This means that even if you run every single WotLK heroic dungeon in a day, you can still choose the random heroic option to continue running WotLK heroics that day. As mentioned above though, the heroic dungeons you have run the most that day will be the least likely to be randomly selected for your continued play by the dungeon finder system.

Does this mean that raid-lockouts are unaffected and you can enter multiple raid instances through the random heroic dungeon finder?
The new dungeon finder is designed only for 5 man dungeons, and the lockouts and accessibility to raid content remains unchanged/unaffected by the "override" in heroic instance lockouts for 5 man dungeons. Source