I am a flickr Guy but I use Picasa also for my personal fotos.
Now i have upgreaded to Ubuntu 10.4 So I installed Picasa 3.0 to my Ubuntu. Its very easy.
Get the approprate .deb file for that.
Download the deb file from http://picasa.google.com/linux/download.html#picasa30
I downloaded picasa_3.0-current_i386.deb
Once this is copied
dpkg -e picasa_3.0-current_i386.deb
Here you go. Picasa is up and ready to use.