I feel your pain on the lack of expandability but do you realize that the upper end iMac can get 3Gb of Ram now? Hopefully it will be 4Gb with the next model. Also, you can get a 500Gb hard drive as well. How much internal storage do you really need if you aren't a pro?
I agree that the chin is not attractive on the iMac but I can look past that. Keeping the 20 or 23" display could be nice, but then again, selling the iMac and getting 3/4 of what you payed for it a couple of years later is nice too. What other desktop PC can say that?