Picasa has one big known bug which has not been resolved for the last year, that is it's viewer executable is not killed when you close it. So, if you want to use it to view pictures, you end up with tens of threads left open. Each will take 5MB RAM circa. It happens on both 32 and 64 bits versions of Windows since XP on, and the net is full of complaints not being addressed, so far.
Consider that my PC gets rebooted only when updates require me to, so basically I end up with tens of dead threads taking each 5 MB of ram...

Also, viewer ins not completely integrated into the rest ofthe software, and moving from one to the other is annoying (I want to be able to see an image full screen, then go back and browse, and it requires way too many clicks. There are other minor things. Essentially, I like it overall but there's some room for improvemente and since I don't mind spending some money on a product to manage my collection and view it, I am hoping something is in fact out there.

Lightroom is very nice, I think, but i lacks the "viewing" part, mostly. And face recognition.

I don't know, I still haven't found something that makes me happy enough to stop searching