That New Car Smell... Tainted!

So yesterday I wiped my computer and reinstalled the OS. It wasn't all that painful as I thought it would be. It took about an hour to back everything up to an external hard-drive . The OS re-installation took a little under three hours. Then we get to the bad side though...
What was rather irksome is that it didn't wipe the hard-drive! Yes it reinstalled the OS and reset the registry and she's running like brand new again, but the hard-drive is still slightly cluttered. It copied the old hard-drive (minus things not pertaining to windows) into a folder called windows.old. This contains:

• PerfLogs
• Program Files
• Program Files (x86)
• Program Data (hidden)
• Users
• Windows

So any viruses I might have had before (AVG assures me I had none) could potentially still be there. It also means absolutely no hard-drive space was freed. I'm not entirely sure it's safe to delete this folder or I would have as soon as I saw it. I backed up everything I wanted! Why was this not an optional thing?

Now I've got the program files for several dozen bits of software I don't want and that don't work anyways (it disabled them). Plus there's my old mess of a user folder. All that unwanted is sitting in C:\windows.old\

I wonder how long it would take to delete ~270 gb of data (if I find it is safe to do so).

Update: Apparently this can be done with a disc cleanup. I think I will schedule this for next week (270GB will take a long time!). That gives me time to make sure I've not forgotten anything really really important.

Another interesting thing to note is that it didn't backup things on the harddrive that weren't on the listed folders. I kept all my most important software outside of program files too, so all the following are missing (except in my backups that I did manually)

• Coldfusion
• Perl
• Unreal Development Kit