I just started up Training Center, intending to compare a race I had Tuesday evening with ones at the same site last season. ALL my data was gone. The f'ing program deleted everything. All my .bin files were reset to default.

Now I only have the data that still existed on my 305, basically about 3 weeks worth. Over a year of training and racing data gone.

So, now I know. Back up your Documents and Settings/All Users/Application Data/GARMIN/Training Center/*.