This is the primary reason (out of many) that I didn't get an iMac.
I had a really nice dual screen HP PC set up before with beautiful matched screens. There's just no way to do this with a Mac without going to a far more expensive Mac Pro. So although I've got two Macbooks for my portable needs, I ended up getting another HP desktop, running Vista. It actually blows any iMac out of the water, quite honestly. Came with a really powerful video card, 6 MB of RAM, a terrabyte of hard disk space, built in hi-def TV tuner, etc. All for $1500 with one high res 24" monitor (the second matching monitor will cost you another $400 or so). And Vista has actually been perfect. Not a single glitch after the first six weeks of use.
I only bring this all up with the hope that Apple will get on the stick and bring out a decent desktop without all the limitations of the iMac. Style only takes you so far.