I think my iMac is probably able to run Lion but I will double check to be sure. That is another issue with Apple-they are willing to leave a lot of their customers behind. After Apple went to Intel chips a lot of people were left behind. People who had some fairly powerful Macs were unable to run the most recent Apple operating systems.
I used mostly Apple Computers (at home) for a long time. They were less hassle and there was a time when a person just about had to have an Apple Computer to do any computer graphics. I seriously think that situation is reversed today. My Windows 7 computer is easily able to run my photo printer and my flatbed scanner. Heck, I was even able to run my dedicated film scanner, thanks to Microsoft and NOT Nikon!
I can't get decent prints with my photo printer using my iMac. Back around 1999-2000 I would never have believed that I would be making a statement like that. Now a Mac is still useful in some situations even with the computer graphics field gone, but I sure will not buy a new iMac. For the price of a good iMac I can buy a custom built powerful Windows computer. And for much less than that, I can just upgrade whatever needs to be upgraded on my current Windows 7 computer.
I think Apple needs to pay more attention to their computer users and a little less attention to iPads, iPhones, iPods, and their dream of the mobile computing life that does not fit everybody. When I go on a trip taking photographs I certainly do not want to drag a computer around with me. I work on the photos when I get home. I lug enough camera gear and other stuff on a trip. The last thing I would want to stuff into a bag is a laptop computer. And the last thing I would want to have on some windblown, dusty mountain ridge would be an iPad or a Mac laptop computer.
Few people know this, but Apple desktops are in decline and not just Windows desktop computers. Apple might need to consider this-be careful what you wish for, you just might get it.