Picasa Sync Sucks
Well it probably doesn't suck - it's just that Sync to Web function ONLY functions when you upload an album to the web AND have Sync enabled when you do the upload. When you Upload, it never says - "Oh, by the way, if you ever want to enable Sync on this album, you darn well better use the Sync function to do the upload cause if you don't you'll get duplicate web albums!"
Obviously the programmer that implemented Sync had never used Picasa or at least never used the Upload feature otherwise s/he would have realized that there was a HUGE usability problem if you ever want to enable Sync after you do the upload.
Anyway, the Sync to Web function really needs to be updated to allow enabling Sync after the album has been uploaded. If the album has already been uploaded, you just need to ask the user which version (PC or Web) is the master and make the other version match it. And then maintain sync from that point on.
What I invariably do is upload the album, then add/edit/delete and then realize "Oh I need to update the Web album, Sync should do that". Ooops, now there are 2 and of course I shared the 1st non-synced one with friends and family. Now if I want to use Sync, I have to delete the 1st and re-do the sharing to friends/family to make sure they get the latest.
Oh well, why don't they ask the users how these things should work before they start complicating our lives with features that miss the mark????