Adam Scheinberg has written a great little review/overview of Flickr and Picasa Web Albums. I’m been messing around with Flickr for some time now, and fiddled a little with Picasa Web.
I’ve been using the Picasa desktop version for quite a while to sort all my pictures and I’m pretty happy with it. The biggest issue that I have with it is that you can only give a photo one tag, or “label” in Picasa parlance. That’s a real bummer when a picture fits into multiple categories.
For instance, when we go on vacation and my wife takes some great pictures of the kids, I would tag those photos with “kids,” “vacation” and “family” in Flickr. With Picasa (both the desktop and web versions) I have to choose one label to which the picture will belong.
For my money (and both services are free) I’ll stay with Flickr for my photo-sharing needs.