Script attack for capturing your browser history
This page < Bookmark button test page > contains a nice demonstration of the ability to retrieve your surfing history from your browser. In this case, it looks for any social bookmarking sites you many have visited in the past. Obviously this could be extended to look for any other sites you might have visited. For example, this would enable an attacker to target phishing attacks at you based on the bank websites you actually visit. This shows once more the doubled edged sword of browser functionality. The scripting capabilities make possible such things as Google Docs but also enables this kind of attack. They go hand in hand. The more power you give to the scripting language the more opportunity there is to abuse that power.