I was never able to play in random dungeons after the new DLC dark brotherhood. Second patch was launched and nothing.
I usually play as Tank so the wait is about no more than 10 minutes... well, I have been logged for hours and nothing. Aren't you annoyed with that too?
No information when it will be fixed. For me it's an very important part of the game, I usually played one or two dungeons daily. Thinking in go play WoW or other game and quit this.