I didn't say it is flawless. I said the issues are overblown. The computer was slow with Lion - unacceptably so IMO. With the upgrade to ML, by and large the vast majority of framerate issues are gone. The little bit of stuttering that remains seems to be due to the iGPU. If I force the machine to use the discrete GPU, it works great. Even without it, there is very little that actually causes lag.
Why are there threads like this? Because people (such as yourself) blow the issues out of proportion without even spending time with the computer themselves.
And the vast majority of people don't give a crap about minor stutters here and there. They just care that the device looks "sexy". If the stutters bothered them that much, no one would buy an iPhone 4 anymore, and no one would have bought 2nd had iPhone 3G's back in the day. But instead, both devices kept a significant portion of their original values.