I got a Macbook Air from work. Stuck Ubuntu on it, and a big kayak sticker over the Apple logo. They aren't getting free adverting from me. (One fanboy looked noticeably upset when he saw it running Ubuntu).
Fanboy-ing aside the benefit of OS X over Ubuntu (et al.), to me at least, is that it is more stable, still unix and there is much more software available for it that doesn't require debugging/building/re-building, etc. Ubuntu is fun for playing with, but when I need to get work done it tends get in the way eventually.