I know that I am staying with the G5 that I have using CS4. When my time for upgrading my Adobe product reaches version CS7 - I will be making a decision of whether to stay with Apple.
I'm not a power user. I want a mid-level tower with it's own dedicated video card, and space for two hard drives, with no chimping out on available ram slots. If Apple cannot make such a machine for around $1,500 - $1,700 Cdn$ - then I will be poking the tires in the Windows world. There is no reason why they cannot do this.
As a potential customer I will not accept being told that the iMac is all that is offered for this price range. When they dropped the matte screen for glossy only iMacs - what was barely tolerable for someone that wants more options for expandiblity was not worth putting up with. Apple refuses to listen to a segment of its users that want matte screens. I want to service basic stuff with my computer and not have to have someone replace hard drives (if I understand what others have said about this issue correctly).
Uh, if Adobe's direction for Lightroom is any indication, the PowerPC is dead to them for any future versions, including CS5. Get on the Intel train now.
I actually know quite a number of graphic designers and they've made do with iMac's. The i5 and i7 have more than enough horsepower for the Adobe apps they use and they position their Mac's for low glare or use black fabric behind them. Many simply use a 2nd matte screen for critical work.
I'm not an iMac lover either (personally hate the glassy screens), but if you don't need more than 2 monitors or the hardware expansion bus, you can make them work for the majority of tasks (yes, I know there are exceptions). And sadly I think that's enough for Apple at this point and the days of expandable towers as a focus are numbered with them. They'll simply get you to upgrade every couple years as they slowly ooze new hardware (like Light Peak) into future all-in-one products.