I have upgraded from W.7 to W.8 Pro. A few programs were listed as incompatible with it. There was a message about CorelDraw X5 being incompatible but I chose the option to 'run it without help' and found that the program worked OK anyway, apart from its twain (scanner) driver being inoperative. I can put up with that. Help just directs you to the software site to buy an upgrade. Sandboxie is another program that W.8 advisor said was incompatible but that appears to work OK too.
Bitdefender, the installed security suite, needed uninstalling and re-installing to get the autoscan (idle-time scan) function back.
I bought the W.8 Pro upgrade from the Microsoft site £24-99 + V.A.T) and chose to keep files and programs intact. The 'Windows.old' and other backup files have now been removed using the Windows 'Clean up system files' options. If I need to go back to Windows 7, it's all there in a disk image that was made prior to the upgrade.
A folder ends up on the C: drive called 'ESD'. This contains the W.8 installation files. Windows 8 can be reinstalled from the .exe found within this folder. I believe it's also possible to make a bootable installation disk from it, so think the folder is best copied and kept before any clean-up of the system. In retrospect, it might have been better to download W.8 using the 'Install by creating media' option. This might have given me an installation disk. Not an insurmountable problem though.
W.8 took some work to get it running efficiently but it all seems OK now. Difficult to get used to IE10 in its full-screen W.8 mode but it can also be used in the old way in a window with a 'Close' button. Other browsers run OK on the system.
Worth mentioning is that the included mail program doesn't support POP mail. Webmail and IMAP are supported. However, Thunderbird or other e-mail program can be installed and used. W.8 doesn't have a DVD player either. Data can be but on a DVD/CD but it won't play a DVD video or film
Regarding this: Those who have purchased Windows 8 Pro can download the Windows Media Center Pack for no extra money. It's a time limited offer. Request a key from here:
Add features - Microsoft Windows
Other than that, I believe any popular media player can be used. VLC will work OK