When I had the 7100i, and loaded the latest OS, I would get the registration message at least once or twice a day..... I personally think it's something with the OS that is making it re-register.

The Enterprise Activation is used to connect your BB to a corporate Blackberry Server (i.e., at your place of employment). If your work doesn't have a BB server (aka BES) then you can just hide the icon.

No, there are no updates.....and there probably won't be any, unfortunately.