On Cataclysm Classic the level ranges shown on the Random Dungeon Finder interface are not accurate to what you can actually queue into. The level ranges are a lot more tight and strict than portrayed. For example, you are level 28 and have a level 29 in your party - it will not let you queue for Scarlet Monastery Graveyard even though you are both in the shown level bracket (28-34). The back-end level brackets seem to be outrageously small, which extends queue times for those wanting to use the random dungeon finder.
There are also odd behaviors around certain dungeons. For example, I dinged level 15 last night and the two options for dungeons I could queue into were Ragefire Chasm and Deadmines. Upon dinging level 16, the option to queue into Deadmines went away even though I was still in the shown level range for it.
It would really be awesome to see this problem fixed in time for the MOP re-release as it makes it really hard to queue random dungeons with friends.
I experienced these issues on Wholewar - Faerlina Horde