WebCards is the latest browser extension which takes advantage of microformats. Built by the chaps from whymicroformats, it exposes microformats embedded in pages - events, contact details that sort of thing. It is still in Alpha/Beta at the moment, but you can sign up for notification when it launches (initially for Firefox) - though I wish they’d get rid of the annoying pop-up about a license requirement just for viewing an information page.
With Firefox looking to embed microformat support in version 3 and Microsoft also taking notice, it looks like this small but powerful tool is about to get a lot more attention.