I love using Picasa and am totally dissapointed to find nothing of the sort in Ubuntu and not being about to download it...anyone know how to?
Google used to offer a Linux download for Picasa, although it was just the Windows version bundled with Wine. In april 2012 they discontinued it, but you can always download the Windows installer yourself and run it with Wine. There's info in WineHQ.
As Swarnendu Biswas said, there are very good alternatives. Shotwell (Gnome), Gwenview and digiKam (KDE) available in the repos, and XnView has a beta multiplatform version than can be downloaded here.
This is Picasa 3.0, I have not tried installing it. Have you tried running Picasa for Windows with Wine or CrossOver? That should work.
Okay, you are asking about downloading Picasa for Linux. So the following does not really answer your question, but you could still try the following pretty capable alternatives. You can expect to have new releases in the future for these applications.
Shotwell is not bad, you can use plugins to also publish photos to online websites.
Gwenview is a KDE application and another alternative, and is pretty good too. Only thing is that you will need to install quite a few KDE dependencies with it.
XnView is also pretty good, I have used the Windows version a bit but have never used the Linux version so can't comment much on it.