It would be awesome to be able to group bookmarks under another bookmark (instead of a folder). This would serve the same purpose as using a folder, but it would save an extra click. Either click the top level bookmark or hover over it to show the bookmarks grouped below it. (ie If you use Gmail 99% of the time but want your AOL and Outlook mail close by as well.)
Either this or allow users (that have a lot of unlabeled bookmarks) to define a custom folder icons.