I know the freezing should not happen (I've had it a few times and it is very annoying), but I just thought I'd let you know that when it does freeze, you don't have to do that restoring files thing when you turn your PS3 back on. If you press circle when the corrupt files screen comes up (or whatever it says when you turn your PS3 back on), it skips the process.
You may think you need to do this (because it comes up), but you don't, I've skipped it many times and nothing is different, no files were corrupt. (This will save you some time just waiting for it to restore the files).