Google released a version of Picasa for Linux, using a version of Wine modified by CodeWeaver.
The page where you can download the software is http://picasa.google.com/linux (for the moment, the page gives a 404 error outside United States, but you can access it through a proxy).
Google said that Picasa should work on any Linux system with Intel 386-compatible processor, glibc 2.3 or greater, and a working X11 display system.
There is a group about Picasa on Linux and there is a link on Google Labs visible only for US.
Direct links: RPM | DEB | BIN.
This version of Picasa lacks CD Burning, export to TiVo, Hello instant messenger and has A LOT of limitations:
* no motion-compressing codec => huge movies
* no MP3 code => no sound in slideshows
* no video indexing
* weak browser and email integration
* the opening Picasa dialog has a spin loop and consumes a lot of CPU