How about '8.1 just totally broke explorer?' Cookies don't work properly (i.e. log in on main page, go to sub page, and hey, you're not logged in!) the 'open/save' dialogue just kinda ignores button presses, download links aren't resolved through (instead of asking if you'd like to open or save foo.zip, it asks if you'd like to open or save download.php?fileid=1345 and then ignores your button presses).
Resetting doesn't help. Removing/adding from windows features doesn't help. Can't reinstall, as it's baked in. Firefox works fine.