One thing to beware of - your system partition must be 300Mb or bigger for 8.1, or it won't install. Windows 7 only needed 100Mb and so some systems, mine included, were set with that, and it needed a bit of partition twiddling to expand system partition before it would install.

Other than that though I'm a happy 8.1-er.

It's a good update - really lives up to the tag of 'what Windows 8 should have been'. There'll be some who still want to run Start8 and the like, and that's their choice, and Mac and linux fans will hate it because that's what they do all day; but I've been running with a shell script to go straight to desktop and a homebrew start button taking me to the apps menu for a few months now in preparation for 8.1, and once you're used to that change of control features you're just fine (and the new sort and config options are a great bonus).