Beware of Windows 10.

Microsoft are being very cagey about the licencing terms. At this stage it appears that accepting the "free" upgrade will extinguish your (bought and paid for) right to use your copy of Windows 7 or 8 and you will be stuck with 10. So why worry if 10 is OK? Because they look as though they are positioning 10 be morph into a subscription model - i.e., the "upgrade" will be free but then you will have to pay a yearly subscription forever afterwards. Nothing is set in stone yet and Microsoft are keeping very, very quiet about the details, but DO NOT "upgrade" to Win 10 final release until they have made the fine print public and people you trust have had a chance to look at it carefully.