http://www.pcworld.com/article/2950649/windows/9-reasons-not-to-upgrade-to-windows-10-yet.html
"9. You don’t need the pain of early adoption
No matter how widespread beta testing is for a new operating system, it can’t uncover all the bugs and gotchas. A new operating system hasn’t been tested on every possible piece of hardware, with every piece of software, and with every hardware/software combination. People who upgrade immediately are the guinea pigs. They’re the ones who feel the pain.
If you’d prefer to go with an operating system that’s had enough time for a shakedown cruise, wait another six months before you upgrade."