It's tough, I'd kind of like to replace my current windows ultraportable and I have a portability issue with my macbook pro (original revision, 2.16Ghz). Thing is I could put together a 2.2Ghz, 4GB RAM macbook for less than the money they want and it'd be pretty portable.
It's a tough call, I think it'll appeal most ot those who have imacs or mac pros, it's the obvious companion for those systems.