iPLM has once again proven to be an indispensable app. I sync some of my iPhoto libraries between Macs using Dropbox. I got a warning that my 50 GB Dropbox was 100% full, yet the Dropbox folder on my Mac was only showing 38 GB in size. It turns out the problem was my iPhoto libraries, which had been incrementally upgraded from older versions of iPhoto, and contained alias folders. Specifically, new versions of iPhoto store original versions of photos in a folder called Masters, whereas older versions stored them in a folder called Originals. An upgraded iPhoto library will contain an alias folder called Originals linking to the Masters folder.
The problem is that Dropbox can't tell the difference between an alias folder and a real folder, so it uploads, syncs and stores images in both folders. A 7 GB library on my Mac became a 14 GB library in Dropbox. Fortunately, iPLM includes a function to rebuild an iPhoto library, which gave me a new library with all events, albums and keywords intact (but not smart albums, which were easy enough to recreate), and more importantly, without any alias folders. Now that 7 GB library only takes up 7 GB of space on Dropbox. Add in a few other libraries, and I now have a lot more space available in Dropbox. I was thinking I'd have to upgrade to the 100 GB Dropbox account, but with iPLM I avoided that and saved $100 a year.