Yeah, I can attest to the style quirks.. Damn TabPanels :(
Lets hope the bugs continue to get ironed out. I know 1.4 will fix quite a few of the minor things.
I think the big deal is the RPC stuff with GWT. While it still has a way to go in terms of customizability, it is extremly powerful none the less. As far as Flash + GWT, I think its pretty sweet doing asynchronous calls via JSON messages between the two. Quite a powerful combination..
It alleviates some of the cross-browser headaches, but doing anything nontrivial can still hit browser differences, especially with styles and layout.
The only viable browser-worry-free platform seems to be Flash right now.