The coolest thing it does is give you a new way to quickly access bookmarks - hit F4 and a search widget pops up. Hit some keys, and your bookmarks are filtered on the fly. Very cool. You can even configure it to close the floating widget after opening a bookmark.
It somehow modifies the View Source window, so that source code for a page is properly syntax highlighted (and you can set any font you like as well).
It also does some other useful things, like optionally forcing all links targeted at "_blank" to open in a new tab rather than new windows. It also provides better searching/filtering of browser history (that's how I quickly found the URL for John's post - I last saw it this morning and just hit the history search to pull it up quickly).
Stand probably does a bajillion other things. The website looks like it is in Japanese, so I can't read the official description or changelog, but it works GREAT!