I was worried at first about updating to 7.2.1 ... but when i seen all the problems others were getting it all had a pattern. They all had there current live sites heavy moduled. What I did was disabled all other modules that I purchased from the market. Then I installed the update and it worked perfectly.
Once I tried to install the market purchased mods again I had certain errors so left them off. Then it is best to let the mod creator update it to fit 7.2.1
But if your website is live and heavy moduled then I can see how frustrating it can be it happen to me with 7.1.6 , Although I have spotted 2 graphical glitches in 7.2.1 that did not happen in 7.2.0