I own an Edge 305 and a Forerunner 310XT. My wife owns a Forerunner 305. We have separate OS X user accounts and separate Garmin Connect accounts. I successfully set up my two devices to sync with Connect a few days ago and, this morning, successfully set up my wife's device. As before, I had to manually remove the Garmin preference files from the Library folder because your programmers have not properly tested the software.
Now that my wife's OS X account is logged out, I have logged back in as myself to sync my Edge. Surprisingly, Express has now taken me back to the "Get Started / Take the Tour" window. Please tell me that I am not expected to have a separate Mac for each user as I am now seriously beginning to wonder whether your programming team is being paid to encourage us to buy Suunto devices instead.