Hey Guys,
Only 1 of 4 machines in the house are upgraded to 10. Do have to say the upgrade experience was seamless (for me), but I've helped quite a few others who had problems. You have to upgrade in order to get W10 free... So the preferred method for me is upgrade, ensure activation, then format, perform clean install of 10, <create full disk image back up>, Reinstall my programs, make another back up, then weekly back ups.
Can definitely confirm what dmdilks states as far as activation goes. Gone are the days of entering a product key, once activated, future installs on the same hardware will activate automatically. Pretty cool of MS, but, and yes there's a but. Besides losing some features (won't go into them) the breech of privacy is pretty steep with 10. Sadly cortana isn't enabled, Mail doesn't get to read my messages and the calendar feature doesn't get access to my contacts. We all use windows differently. I used ghacks guide to disable most of the telemetry gathering updates in 10 which are also being pushed out to 7 and 8.1. I'm not paranoid, just conscious of privacy. You pretty much give up the farm accepting the EULA, but I'm not going to fall over and hand it to them. Ultimately, you lose some anonymity when you move to 10, and its a decent OS, but I'm not ready to give up 7 or 8.1 just yet.
Absic's observations are also spot on. Here's 10 and with it comes... and you get... and well, we've decided that this is going to be the default program for.... However, again, I think MS did a pretty good job with 10. Certainly better than Vista or 8 when we all saw the Metro interface for the first time. Am I going to jump ship and adopt it on all my devices, no. This is one example where your free entrée comes with some not so good sides. Definitely worth trying though.