I am favourable on the MacBook Air and it's only half right.
The design/style/size is A+. With port and optical drive limitations accepted the enclosed battery is a glaringly negative option even with 5 hours of Wireless.
Yet it's still not the device I want to see before I would actually consider buying/converting/using. If I could rotate the screen, (shrink $25-35%) and have it lie flat (call it a tablet with touch), maybe even an iphone mode (ala HTC Shift's Vista/Windows Mobile ...
I downloaded it immediately and have been very happy with it since. The page rendering speed is very much improved being noticeable from the very first web site I loaded. It appears stable (Vista/OSX) and feature complete in the visible areas that they list as improved or new.
If you have important extensions installed, most if not all will not function after the upgrade. Personally the only extension I really need day to day is GMarks and there is a compatible ...