WhatTheFont is still a work in progress: One serious limitation of the app is the iPhone's camera, which has a fixed focal length, so capturing anything but the largest fonts from a printed page is all but impossible. And in a highly unscientific single-user test, WhatTheFont failed to identify 3 out of 4 typestyles captured from the MyFonts website itself. (Sans-serif fonts seem to work best.) But even when getting it wrong, WhatTheFont's list of suggestions is interesting and easy to read, and usually close enough to point you in the right direction. Plus, there's a forum on the MyFonts.com site, where you can use your PC to upload any urgent or lingering puzzlers.
WhatTheFont may be a public service, but it's also a business: WhatTheFont and MyFonts.com are owned by Bitstream Inc., the huge font and e-publishing conglomerate. Odds are, if you ID a font, you may also want to purchase it, and Bitstream will be happy to oblige.
Image via Flickr, Creative Commons: *bene*