By posting User Content to any part of the Site, you automatically grant, and you represent and warrant that you have the right to grant, to the Company an irrevocable, perpetual, non-exclusive, transferable, fully paid, worldwide license (with the right to sublicense) to use, copy, publicly perform, publicly display, reformat, translate, excerpt (in whole or in part) and distribute such User Content for any purpose on or in connection with the Site or the promotion thereof, to prepare derivative works of, or incorporate into other works, such User Content, and to grant and authorize sublicenses of the foregoing. You may remove your User Content from the Site at any time. If you choose to remove your User Content, the license granted above will automatically expire, however you acknowledge that the Company may retain archived copies of your User Content.
The only silver lining here is that if you delete your photos, Facebook can no longer use them for free and they're yours again
Here's an excerpt from the Flickr's Terms of Service
Yahoo! does not claim ownership of Content you submit or make available for inclusion on the Service. However, with respect to Content you submit or make available for inclusion on publicly accessible areas of the Service, you grant Yahoo! the following worldwide, royalty-free and non-exclusive license(s), as applicable:
With respect to photos, graphics, audio or video you submit or make available for inclusion on publicly accessible areas of the Service other than Yahoo! Groups, the license to use, distribute, reproduce, modify, adapt, publicly perform and publicly display such Content on the Service solely for the purpose for which such Content was submitted or made available. This license exists only for as long as you elect to continue to include such Content on the Service and will terminate at the time you remove or Yahoo! removes such Content from the Service.
The important part here, in my opinion is the section that states that this license that you're granting Flickr/Yahoo covers the activites they list as long as they're "solely for the purpose for which such Content was submitted or made available". By my understanding this means that the photo you upload to Flickr, can't be used in a television ad for Flickr, whereas the photo you upload to Facebook can. Here's the relevant section of Flickr's Terms of Service before being acquired by Yahoo.
We claim no intellectual property rights over the material you provide to the Flickr service. Your profile and materials uploaded remain yours. You can remove your profile at any time by deleting your account. This will also remove any private images you have stored in the system. However, by setting your uploaded images as "public", you agree to allow other Flickr users to view and share your images and you therefore agree to allow us to display and store them.