I did not noticed any major change in functioning of modem / router, only some graphical interface and viewing changes. Some menu and configuration settings changed now & can be easily accessed. After upgrade you will find all settings and configurations by typing http://192.168.1.1 hence http://192.168.1.1/home1.html dose not required any more as earlier.
I even tried it on Nokia Siemens Networks's C2110. Firmware of Nokia Siemens C2110 now changed and it is showing ZXDSL 831AII as modem. Though firmware worked on C2110 and my modem is working fine, it is not advisable to do upgrade on nokia siemens C2110 at all.