I have used Picasa on multiple OSs, but it seems too intrusive by automatically detecting and indexing all documents, it has found and indexed application based images which I don't want visible in my collection, the only feature I like is the ease of uploading to the web, but that is also restricted to a single site.

If you want a good photo management solution that is non-intrusive and easier to manage I recommend digikam, it has feature that I wish were in Picasa.

I find Picasa so much better than competitors like iPhoto. It doesn't have the downside of an xml database on the backend and it doesn't store it all in one large file like iPhoto has (or still does, I'm not sure). It also has good backup features for keeping a recent backup of all your pictures.