Customer support isn't that great for Apple actually. :\ In a lot of my experiences, it's been awful - and those standards were taken even lower when I called my local apple store. I guess it would all depend on who you get connected with on the other end of the phone.... a lot of apple's representatives suck though. I don't understand how they get hired, it's like they just switched to macs and they know nothing about the system.
Anyways, I really would not suggest an iMac. TONS of people have built or bought Hackintoshes and they work PERFECTLY under Leopard. You need to understand that. Sure, any update could break the machine, but how likely is that..just wait and see if it broke other people's machines before you update
Building a hackintosh is cheaper... a LOT cheaper... the hardware in it will definitely be more reliable than in an overheating iMac, and it'll also be DESKTOP components inside the box - iMac uses mobile components and I know Apple is known for underspeccing components.
To each his own, but if you want more power for a cheaper price, also more customization, get a hackintosh. If you get an iMac, sometime in the future I bet you will regret it.
I have a tip for you and the iMac though, I say you should wait for the iMac to update to Matte screen - that is the BIGGEST complaint I have about mine right now - after long hours on the computer, for the year that I've had it, my eyes get sore, and they strain often, and I could tell my vision has gotten VERY noticeably worse. This is because of the glass over the LCD panel, the glass flips the display's image upside-down and your eyes simultaneously have to reconstruct the image to make it look right-side-up. This causes huge eye strain and is the last thing you want to do to your eyes.... especially if your vision is not that great in the first place.
I hope this post helps! Good luck.