Just done it on my iMac. I decided to do a complete fresh install to get rid of all the built up junk. Panicked at one point when it said 1 sec to go and had to wait for over 10 minutes until it finally completed, phew !. So be patient.
Its all back with all apps reloaded from my backup and working.
Got to say not over impressed with the new flat look interface look but I guess it will grow on me, its just different. The iCloud bit works well.