Verifying all my sites was a pain (the verification server probably got slashdotted, and when it was working, it wasn’t resolving DNS properly), and took about a week. But now that that’s over, it gives me some useful info. It really helps, to get a view of your site, as google sees it.
Most of the use for me, is the Preferred Domain tool (i.e. make google prefer www.yoursite.com over yoursite.com), and the Site Content tool.
I’ll look into sitemaps another time :-)