I too spent a day doing this. I downloaded Samsung Kies 3 on my laptop, and according to the program settings, it downloaded all my apps and settings etc. to Kies. I then performed a factory reset, followed by a restore from Kies.
I learned a number of things. Firstly, all your important apps need a visit before you entertain this (if possible at least). Some of them just automatically consider this a new device, and if you haven't taken steps previously in order to save all the data, even when all that data is restored to your phone, it feels the need to discount it.
I also discovered that even though the apps had now been "restored" most of them ended up redownloading themselves from scratch when opened anyway.
My biggest gripe however, is how much stuff just got lost in the process. I got all my pictures and files and everything back no problem. However downloaded ring tones etc were not restored, nor any of my homepage settings. Not one. My lockscreen wallpaper and homescreen paper WERE restored, but the number of pages and the icons in them were NOT. All my information from S Planner was restored, as were my alarms and S Note, yet Watch On, not a single thing. I don't know why it doesn't put back widgets where they were or with the settings they had, or all the custom pages (I only had 3 pages total, but after reset and then Kies restore there were 5, one of which was totally blank, the others just like a messy version of how the phone came originally). It also said that it backs up account information, but that wasn't the case either. When Play Store wanted to update an app, I had to re-enter my credentials, and same when Samsung apps wanted to update, I had to input my Samsung details also. It really was a day long frustration-fest, the first time since owning the phone that I had to do anything because an update didn't take properly and therefore a lot of things learned in the process that I just expected to happen which didn't.
So before you go gung ho into this, make sure that every app that has settings or a history that you really care about, has been visited and where possible the information saved and backed up somewhere (be it cloud or computer). Screenshot your layout too, because for whatever reason, this is something Kies either doesn't put back, or messed up putting back. Only when you are sure you can get everything back as you want it should you then proceed with backing up to Kies, then performing the factory reset and then restoring the phone.
Hopefully when reading the advice that was given to me, first timers like myself can now be aware that it isn't simply a case of "backup" and "reset".
Angloshot, I'm sorry to hear about your trouble, after all the heartache and frustration of doing mine, I can at least report that the issue of Touchwiz crashing when trying to move an icon, was cured for me by the reset. I won't be in a hurry to let my phone get the next update.
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