I just tried updating from 1.7.1 to 1.7.2. During the process it said everything but the user_manager plugin was updated (that one showed a red icon). Clicking Next brought me to a page whose contents are "Oops! Page not found submit". All front-of-site pages show that. I tried copying 1.7.1 back over the 1.7.2 files but I still have no functioning front end.