Navigation in the header, ad up top, logo on the left (simple text logo with perhaps the image of the phone will do), one smaller column with search, 300x250 ad, top themes, and recent posts in the forums.
Main content area should show the most recent themes, and then top/popular themes.
1) Keep in mind that the fullsize theme preview image is 320x480 - naturally we'll want to thumbnail that, but also keep the proportions similar!
2) A top bar that allows the users to filter what they see per page and have pagination on the bottom, just like these browse pages: http://alturl.com/kwx2 or here: http://bit.ly/1179s1
Theme detail page will follow the ithemer and skthemer detail page moreso than the opsds detail page in that I'd like a frame of the actual Pre device with the theme thumbnail/preview on top of it, like here: http://alturl.com/jghw or here: http://bit.ly/4oKRuO
It should still the stats (date, downloaded, rating etc), commenting, and if space permits, a similar themes panel under it i.e.: http://alturl.com/hpzk
As for style, I'd like to go with pre colors. The dialer is in hues of green like this site: http://bit.ly/14FQML, though any colors that match the overall look and feel of the WebOS would be good. I'd especially like to see perhaps the main body of the site with rounded edges similar to the way the "cards" appear on the Pre.
You can preview the WebOS at sprint's site: http://now.sprint.com/palmpre/