The site really matches the Mac OS X “Leopard” feel, with it’s purple aurora background, which, if you check, is the actual default desktop background on the current Mac OS. The skyline and logo in the header are PNG images with alpha transparency, overlaid nicely over the Apple background. The header is the most unique part of the design, and it looks quite good in my opinion.
The sidebar is a bit cluttered at the moment, but that tends to happen over time. (I generally recommend taking a critical look at your sidebar every few months and pruning it a bit.) The rest of the site is clean and layed-out well.