[northernpenguin]

Every time you click on Latitude in the menu, it will refresh your position. If it doesn't, make sure you are running the current version of Latitude -- they added the feature around version 3.0

Also, make sure Latitude isn't being closed in the background! If your Windows Phone runs out of memory, it'll close Latitude. You won't be able to tell unless you check task manager because calling up the application restarts it.