Very nice (indeed, nicer than the equivalent window in TMate). However, it needs to be available some way other than through the through the "Windows/Tool Windows..." submenu. It's bad enough that some less frequently needed windows are only available that way (Ant, TODO), but Changes is going to be used a lot more often. I would suggest a menu item under version control. I'll submit a JIRA.
(No, of course I don't have my workspace ringed with toolwindow buttons. Who has enough screen real-estate to waste it like that?)