As far as I can tell, the real reason they made the upgrade, had to do with providing support for Microsoft Outlook Exchange - which was a barrier to purchase. They tossed in some optimizations that were probably already in the can.

The only thing I really notice, as mentioned before, is improved speed in graphics rendering, which lets me breeze through thumbnails.

Picasa is now so fast, it's breathtaking. Even Adobe Bridge CS3 is faster. It's as though I had gotten a newer, faster machine altogether, for a comparatively low price.