If you do large groups it's one floor with 30k xp/floor at level 30 or so, provided no rooms are missed and you don't die.
Some large floors can take 20 minutes, so it's more or less 90k/hr at level 30; not bad.
Besides, dungeoneering is a little monotonous, but hell it's useful for training combat and every skill in the game.
Just as a point of interest, if you plan to do a floor of dungeoneering with friends purely for skill experience rather than combat, I strongly advise taking someone of a much higher level with you too. They can kill off the monsters and mine the higher level ores, catch the awesome fish etc. and sell them.
In less than 10 minutes last night I manged to gather up 100k cash simply by mining stuff, which is incredibly useful for any low level skills which can be purchased from the smuggler.
If you plan to do combat, try and keep all combat levels within 10-20 of each other, otherwise people get killed or left out.