The most interesting part of WebOS is and will be Enyo, the Html5+JS+CSS UI framework.

Seeing that thing change the ui layout from 1 pane to 3 pane simply by having the size of the browser window change is more impressive than anything cooked up by Apple or Google so far (tho Android Fragments UI lib may be close).

Basically, it can potentially go from phone/pmp/pda/tablet to desktop with simply a change of output. And adapt to the new screen area as it happens.