Microsoft have made several improvements to the Windows 8 Upgrade process, in an attempt to make it as simple as possible.
Below you can see the screenshots I took when I upgraded my main Windows 7 Professional based machine to Windows 8 Pro.
Overall my upgrade experience was fairly painless although I had two problems, one of which could have been quite painful:
(i) when I tried to upgrade within Windows 7, it allowed me to download the new Windows 8 Pro files, and then told me I didn’t have the necessary 20GB free rather than upfront
(ii) I think the failed upgrade above somehow screwed up my HDD and it wasn’t detected in the upgrade process. To fix I had to put my HDD in another machine to fix, which meant wiping the disk.
This would have been a disaster if I didn’t have a backup of all my files.