I have about 420Gb on my MBP HDD. I have run backups using both Time Machine and Carbon Copy Cloner. The backups are both less than half the size of my HDD data. I did not select any sort or encryption or compression. I ran a permissions repair on the drive (it only found 2 small issues anyway) and have gone through the backups and the source drive and done a stare and compare as best as I could without finding any major discrepancy. Any ideas what could be going on?