There's been an interesting discussion in both the mainstream media and Facebook's blog (there have been two entries) about Facebook and copyright law. My three cents is that the only thing that Facebook needs a perpetual license to is an email that I send to a friend via Facebook. I think it's weird that they'd even need this, given the fact that one normally doesn't think of email as copyrighteable. If I send an email on Gmail to my friend on Yahoo!, am I really granting Gmail a license to copy my email and send it to my friend? Ordinarily, I wouldn't have the need to claim copyright on an email I sent. Even if I was sending my friend a manuscript for a book I was writing, could I then sue Gmail for copyright infringement? I don't think I'd have a cause of action.
Anything else that I post on Facebook, like a wall post or photo, can be deleted. Therefore, any license I give Facebook for posting something like that should be revocable at my will.
I wonder whether someone who sued Facebook for copyright infringement for redistributing his or her pictures would even have a cause of action (so long as Facebook posted them in compliance with his or her privacy settings). I guess Facebook is covering itself, but are they going over the top?
Flickr's terms of service are pretty clear. Once I remove my content from Flickr (which is owned by Yahoo!), Yahoo!'s license to display and/or distribute this information is instantly revoked. Sometimes, as when I submit content to a Flickr-sponsored group, the license, by its terms (you'll need a Yahoo!/Flickr account to see these terms), expires at a certain time.
Google's answer to Flickr (Picasa Web), on the other hand, has much broader (and less favorable) terms for me as an end-user. If I upload a photo to Picasa Web, under the terms of service (Section 11.1), I give Google what essentially amounts to an irrevocable royalty-free license to display my information. As a result, I don't use Picasa much.
It's interesting to see what at tangled web is woven with all these license agreements. It also shows the importance of reading license agreements.