I really do like the new iMacs, however a G5 1.8Ghz or 2.0Ghz Dual Processor tower used with any existing display would give you way more computer for your dollar.
The G5 towers are readily available with the faster 128 & 256MB graphics cards and far more upgradable for professional use.
If you simply must have a flat screen display, the market is wide open.
The iMac's 64MB graphics card is soldered into place, so upgrading later
may not be so easy.
No one is sure how the vertically mounted iMac Superdrive will hold up
over time. The G5 tower's horizontal drives are well proven.
The iMac's all in one design is very nice to look at, but one should
consider it's limitations for professional use.
Best of luck on your decision.