Personally, I can see a use for this, but I'm not completely convinced by the style rules that can't be overwritten. I'm all for maintaining a semantic web, but not if it stops me from making an element look just the way I want it to. Inputs in CSS always used to be a headache because of native browser styles that meant overwriting them could be a pain, especially for the old and decrepid Internet Explorer 6. This feels a little like that scenario come back to haunt us.
However, judging by the HTMl5 Spec on the search type not a lot needs to be done with it and it more represents a placeholder for a more semantic based site/web search. I do, however, quite like the idea of a native quick-search functionality that shows the latest x number of search items.
I guess we'll have to wait and see what happens...