UPDATE (1-19-12): I’m going to leave this post up, but feel free to completely ignore it, as much more information has recently come to light because of some nice e-mails from a guy named Don. It would be best to check out his lengthy explanation of the current situation with Picasa on multiple computers here. The complexity of the situation has me simply wanting to find a different solution for organizing and sharing my photos. Ugh.
For being such a pioneer of the web/cloud, Google has created a photo solution (Picasa) that is mind-bogglingly single PC based. Even the “sync to web” feature only allows uploading of photos to the web… it’s barely “syncing” anything at all! Your PC simply remembers what photos were uploaded and will update the photos you uploaded when you make changes on your computer. They only recently made changes that will ask you if you want to update your computer if you delete a photo in your web album (before, it didn’t even do that!).
And if you store photos on multiple machines, you’re really screwed. That is the impetus for this post.
Picasa uses .ini files to keep track of changes made to your photos (this is definitely a good thing, as it employs non-destructive editing, i.e. the originals are not altered). As a result, changes you make to photos on one of your computers will not show up on another computer. Even worse, if you have “sync to web” enabled on multiple computers, you sync your photos between computers, and you tick photos already ticked on another computer for upload to the web, you are uploading multiple copies of the same photo (then try figuring out which photo to delete so as to not REALLY confuse Picasa). Not only that, but changes you have made to your photos are not displayed on the other machines, as they are tracked only in the .ini files.
You can try syncing the .ini files between computers, but this only leads to more problems down the road, and you can never be totally sure you’re actually looking at the most recent changes on the computer you’re using.
This post at Cloud Ave. is a decent how-to solution, but is still not a great solution to the overall problem (as there are pitfalls all along the way and it doesn't really allow for mirroring your photo collection on multiple machines). It employs a workaround in which one computer will act as the server, and your other computers/user profiles must feed from that main computer on your network. But what that means is that if you are out in the world and make updates or changes on your laptop (not the “main computer” at home), it will freak out the system once you get back to home base.
While the Cloud Ave. solution is not a total solution, it does illustrate how incredibly simple the solution to the problem is. If Picasa stored your .ini files in the cloud (in your online web albums/profile) or at least synced to them there, the problem would be COMPLETELY solved.
I have NO IDEA why Google has not implemented this, as there are obviously thousands of people who use Picasa across multiple machines. Get to it, Picasa team at Google.
Meanwhile, I'm thinking Microsoft Live Mesh (or possibly a Drop Box folder, though Googling the issue seems to turn up a plethora of problems) is the best current solution. If I use Live Mesh to sync my master "Pictures" albums on multiple machines, Live Mesh keeps everything (including Picasa .ini files) synced. The problem is that you have to either sync ALL your photos (which for me is terabytes of data), or set up syncing for every single sub-folder in your Pictures library (which means hundreds of folders). Since I don't want every single picture I own stored on my laptop, I have to go the "set up every sub-folder route," and Live Mesh is horrible for addressing hundreds (even thousands) of sub-folders, since Live Mesh lists every single synced folder in one long list and has no way to group or categorize things. Using Live Mesh also means syncing everything across the web (not your local connection), so it's incredibly slow (you can mitigate this a bit by making sure your folders are first synced across all your machines before taking Live Mesh live).
I wish I had a perfect solution to share here, but for the time being, it looks like there isn't one. Blurg.