Steve Borsch has an excellent blog entry on why using Picasa's web album is a particularly bad idea -- because posting your images on it gives away all of your photograph's duplication rights to Google, without compensation and in perpetuity:
Google claims no ownership or control over any Content submitted, posted or displayed by you on or through Picasa Web Albums. You or a third party licensor, as appropriate, retain all patent, trademark and copyright to any Content you submit, post or display on or through Picasa Web Albums and you are responsible for protecting those rights, as appropriate. By submitting, posting or displaying Content on or through Picasa Web Albums, you grant Google a worldwide, non-exclusive, royalty-free license to reproduce, adapt, distribute and publish such Content through Picasa Web Albums, including RSS or other content feeds offered through Picasa Web Albums, and other Google services. In addition, by submitting, posting or displaying Content which is intended to be available to the general public, you grant Google a worldwide, non-exclusive, royalty-free license to reproduce, adapt, distribute and publish such Content for the purpose of displaying, distributing and promoting Google services
"Promoting Google services" is very vague. A coffee table book about Google could be construed this way. Definitely an advertising campaign -- how pissed would you be if Google used your photograph on billboards across America and didn't pay you a penny? They have every right to since you gave them that right.
Furthermore, this is hidden in the Terms of Service which no one reads. How many other photo sharing sites have similar rights grabs in their TOS? Previously, I've blogged about why you should never enter most photo contests, but now it appears you shouldn't ever post anything on the web unless you own your own server.