I'm not a fan of v20 right now. GUI edits gone, my config was deleted, my cache was removed and I have to redownload stuff from scratch. I don't get the whole My Documents thing and why if it copies the files to there it leaves them in the old folder. And whats with the launcher, its weird?
Badspot explained within the official topic that you apply GUI Edits as Add-Ons, now. Your config shouldn't have been deleted. Mine didn't seem to be moved, but you can just copy the old one to the new location and it works. I didn't notice if the cache was deleted, but with the new cloud downloading, he probably thought it best to download anew from this cleaner system. It uses My Documents since they circumvents some falsely activated Windows protection that prevented some features of the game which most new users couldn't figure out how to manually work around. It leaves them in the old folder because, if there are any mistakes in the process, who wants to hear "It corrupted all my Add-ons, including my private ones, and deleted the originals!" when you shut off mid process. The launcher is meant to apply minor updates and fix stuff you might have broken like a moron so there's less whining about things here. He couldn't do that within the game itself.