I am running the same setup. I bought the LED Cinema Display to use with my MBP, but swapped it over to the iMac later. It's a great setup. The height difference is not massive, but I do find it a bit annoying. I just need to find a solution more pleasing than a book under the LEDCD.
My next step is to buy some speakers, though I am not as much of a hurry, as the iMac speakers are better than I thought they would be. Certainly better than those in the LEDCD. Still, I think I will be picking up the Logitech Z-5500 set to here in a month or two.