Just did some math on the reported disk space just to make sure I wasn't missing something and here's what I got.
A 500GB disk has got 500.000.000.000 Bytes. Dividing is by 1024 3 times I get the reported 465GB. Could it be that on the old 45GB disk I was using 40 GB and the OS reserved was around 10% (4,5GB)?
In that case, on the new 465GB disk, the OS would be reserving 46,5 GB (10%) plus the 40GB that I was using previously, that would amount to 86,5GB. Ok, the PS3 now says I'm using 100GB which isn't that far off my calculations, but even so, there are more than 10GB missing and why the hell would the PS3 need to reserve almost 50GB?
Does anyone know for sure how much is the OS reserved disk space?
I'm going to try those solutions you guys mentioned as soon as I have some time.