Win10 is a free upgrade for 7 & 8 users. It'll be out officially at the end of July.
http://kotaku.com/windows-10-will-be...nth-1708127315
My boss has been using it for the last two weeks (we're an IT consulting firm) and it's certainly much better than Windows 8. I'll probably be upgrading my office desktop in the next week or two so I'll post some feedback here after spending some time with it.
For home use, there's probably no reason to leave Windows 7 in the near future.