I find it entirely unusable on a Macbook touchpad, and even worse with a magic mouse. Sometimes I forget and go to the site, only to have it freak out on me part way through trying to do whatever I'm doing, while lagging like crazy of course, because at some point Google stopped giving even half a damn about performance, company wide.

Google Music kicks on my fan after a while. The only other thing I run that does that is Kerbal Space Program. One simulates space flight with nice (ok, decent) 3d graphics, the other plays f*cking music.