I did a quick search of the Google Market with the term "Bluetooth Sync" and there seems to be a lot of apps that do that.
It looks like most of them require a "Paid" version to do media files (Pictures/Music..).
But, I didn't see any right off that did it automatically. I only looked at the first couple of apps though. So, you might want to read through them and see if you find one that meets your needs.
However, I will warn you this... What you are wanting can REALLY kill your battery. Bluetooth file transfers are slow and take a LOT of battery power. I would suggest one of the apps that sync over WiFi rather than Bluetooth. You have a larger range, faster transfer, and less battery drain.
Going one step beyond that would be setting up a Free (2GB) Dropbox account, and download the free "DropSync" app that will automatically sync a folder over the web. You can set this to only run when you are connected to WiFi. However, it will not only serve the function, but the files will be "Backed up" on their servers as well. You just have to add the dropbox app to your PC and set up a folder to sync with.
Just my opinion on the matter.