Many people have said that a hard reset without restore is the right thing to do. Many others have said that after a hard reset and no restore their problems have stopped.
If you install 8.1 on top of your 8.0 settings then it can make the apps/phones go a little mad as they get confused by both OS
I have put 8.1 on all my phones listed in my signature and none of them has had a problem except for the first 2-3 days of the battery being bad, WiFi sense and on my 1520 Cortana got stuck but only once and hasn't happened after I removed Cortana's live tile.
Last week I used Nokia software updater for retail to get one of my 925's back to 8.0 and after I restored my backup made before I got 8.1 the day it was released and after leaving it to settle for a few days my phone went mad with reboots, battery only lasting 4-5 hours, freezing and getting extremely hot (I mean really really hot)
Then I did a hard reset and I restored my apps from a backup and again waited and the problems were still there 3 days later except for the rebooting but it had a new problem of when I hit the lock button it sometimes (3 out of 4 times) would take up to 5 seconds to unlock the phone. Locking it wasn't a problem.
I then hard reset it again and installed all the apps again but not by restoring from a backup. That was Saturday morning and already my battery is almost back. I have had no problems and I left it at home this morning with 28% from full charge last Saturday.
I am not sure if MS should have known this but they should have advised people to do a hard reset after installing 8.1 and to not restore from a backup.