Interesting! Great looking app for being free.
After about 10 minutes of playing around with it I noticed Picasa's preview window seems to darken up my .nef and .dng photos that have Adobe RGB as their color space. It did not change my .jpg with sRGB.
When it first imported my pictures their color levels were as I see them in Bridge, or any other App on my mac, then you could see Picasa's viewer darkening them up, one at a time.
I will play around some more with it, but happy enough with bridge...