I've been using TomTom 6 for about a week and a half now. No "priming" needed. In the GPS settings on the phone (not in the Tom Tom program), make sure Manage GPS Automatically is checked, and under Phone-->Services-->Location Setting make sure Location is turned on. In the Tom Tom program go to GPS preferences and Configure and choose Com 4 and Baud 4800. When you go back to the main screen, set a new destination and it starts working (sometimes I don't get an immediate start until I choose a destination).
HTH. Sorry, I haven't been able to upgrade to 7 so I don't know if that will be different. But I don't want to mess up a working system anyway
