Unless you have windows updates completely disabled, at some point in the next few weeks (if not already) MS will push a 6.5 gigabyte file through windows updater that you have no control over. This is the files to move to windows 10. If you are on dial up, cell data, or set up somewhere where you have little bandwidth or it costs money, sorry, you are screwed. Once the download starts, the only thing that stops it is unplugging from the internet or stopping the update service completely. Soon as you plug in or restart, it kicks back in. So far this is happening even on computers that were not supposed to get the option to update at all.
Not a big deal if you have 30-120mbps at home, but when you are on a 1.5mbps T1 at work with 10 other computers and 4 of them are trying to download 6.5 gigs, it causes problems. Even worse when you connect your cell phone to your laptop to get online only to find you used 6.5 gigs of data without knowing it.
The one computer I want to try win 10 on is my home machine and it has not started the download yet. My other 135 computers are going crazy downloading. Bad time to be an IT manager..
FYI, windows 10 will force downloads of updates and you can't turn off the update service (yet, fix might come after complaints). Also many apps will be ridden with ads (like solitaire for example) unless you want to pay for a subscription. Media player was removed, but I have heard they shipped the final release of win10 with software that will play a dvd. If you have a picture in your My Pictures folder, no matter if it is in a hidden folder, the default background and screensaver will cycle those images, so get rid of your porn before installing or you might boot up and have a surprise waiting on your screen (not good if your wife or kids will be using your computer). Unless you opt out, all your Outlook and Skype contacts will have shared access to your wifi connections. This is a big security hole. There's a few other things I read while searching for solutions to the forced 6.5 gig download that are being screamed about since the big release, but I don't recall the rest.