Eh... A little too late to the game for me. I will stick with Aperture and my website now.
If one is really using and benefiting from Aperture, I can't think of why in their right mind they would use Picasa...
Picasa from what I saw on PCs... It had a couple of minor niceties. In particular, on comparable era computers (I guess this is less of an issue now, with how fast the Core 2 processors are) Picasa seemed to get
much less bogged down by having lots and lots of large images in it than iPhoto did. On a G5, I thought iPhoto was unreasonably slow considering what it was being asked to do.
Then again, over time, I stopped carefully albuming photos and just dumped them into iPhoto when I synced my cameras, for storage. Now on a PC, I, embarrassingly, just dump them into a folder (and use Paint.NET for photo editing). I probably
should install Picasa on my Windows PC.