Just a polite heads-up about Windows 10:
Don't do it.

Can't be bothered to check this, but I hear that if you accept the free upgrade (which they're trying desperately to get everyone to use for obvious reasons), they will disable the key you already own for Windows 7 or whatever.  This means that you won't be able to go back to Windows 7 even if you have the key, because they won't activate it.  There is a reason Windows 10 is free, so I'd read the TOS for Windows 10 very carefully if I were you (then you'll find out why they're doing it).

This will be my only post in this thread, it's just a friendly heads-up that you can either take notice of or not (won't effect me either way).