I've been using Syncplicity to synchronize my portable apps across multiple computers. This may not be the originally-intended purpose for these apps, but it's very useful. For example, if I add an extension to Firefox on my laptop, it's automatically available on my desktop!
The only problem I've run into -- really, just on Syncplicity's end -- is that I occasionally need to clean out some duplicate files. Has anyone else tried combining these two tools?