I have a c7 and I downloaded the latest mobile documents beta from the nokia beta labs and whenever I open it up it asks for my email id to send a beta invite and when I enter it, a dialogue box shows up saying that its "Checking user name" and it doesn't go away, i've left the app running in the background for an hour and still nothing happens. The wifi connection I'm usin works fine with the other apps meanwhile
C7 - Can't get mobile documents to connect to the net
I ended up uninstalling it as it was just too frustrating. When it works it's brilliant but it's just not stable enough yet.
Only problem is that uninstalling knackers your mail widget so you have to do a factory reset. You don't lose your data but it's annoying.