I'm kind of ashamed to admit it (at the end of 2010!), but I did some Objective-C/iOS apps for the first time this year, and I was pretty amazed by how good the Apple dev tools and the iOS simulator actually are.
The other thing which impressed me is kvm, in contrast to Xen.
Ditto on the Objective-C stuff, though personally I've been focusing on Mac OS X rather than iOS. Apple really documents things well, and the Cocoa community is extremely nice and helpful. The shiny glare of quality extends deep into the inner depths of Apple's products.
The other thing which impressed me is kvm, in contrast to Xen.