After more than one day of scanny my photo collection, I noticed some glitches (quite few, I have to say) that show some of the current limits of Picasa Face Recognition. I got a plant mistaken for a face, and I got several faces not being recognized at all in the oldest pictures I have, mostly those scanned from prints.
I also noticed that the "Unnamed" section of the "people" folder is not showing many many faces Picasa did instead identify, so that if you click on one individual picture with faces, often there are many recognized as such - Picasa shows them on the right pane and provides suggestions - but not in the "unnamed" folder.
I see now that, because of this, tagging all faces in my photocollection is a huge work and I am afraid I will never complete it. Still, even as it is now, I am having fun and looking through my photo collection in a way I've never done before.

At this point, though, I need to see exactly where all the tagging is saved, and I need to understand how to migrate from one install to the other. While I usually reinstall at every OS change, or less, I just need to know where the stuff is saved on the hdd and how to extract it. I won't feel safe otherwise.
Does anybody know?

Sadly, it seems to me that Picasa does not offer any customization possibility in terms of where to store what, which is a pity in such a nicely designed, elegant, piece of software!