OS X Backup

Hard to say exactly what the initial huge incrimentals were from, and I don't know what specifically the app backs up, but I'd guess it's probably a cache file or some such that's getting updated frequently, and so gets changed every time.

For example (this is just a guess), if it's backing up your Firefox cache, and that cache is 50MB, then most of that data is going to get overwritten frequently, and so it will end up backed up.

In other cases, files that just get "touched" (just the modification date changed, even though there's no actual data changed, maybe) might be getting detected as changed. This could result in large files getting copied again even though there were no meaningful data changes to the files, just because they were accessed.

 

If you change any of your files, they will be re-backuped, not overwritten. So lets say you have a 1GB movie and you back it up. You later decide you don't need it anymore so you delete it. Your originally backed-up file will still remain hogging up all kinds of space.

This may be your problem.