I tried 10.7 three or four times on my mid-2007 iMac with a Radeon HD 2400. The hard drive has been swapped for an SSD, so the general performance was okay, but I found the animations in Lion to be so sluggish that it made my machine feel very laggy. I'm a heavy Expose user, so the Mission Control delays were unacceptable. 10.6 is smooth as silk, but many of the ML features look pretty appealing. Anyone have experience on a similar machine or graphics card?