The Xbox Gamertag plugin that ships with Motiuon appears to be broken out of the box -- it doesn't show a score, but just says "User passed gamerscore on Xbox live". (I can see empty tags where the actual gamerscore or whatever the variable "[_2]" is supposed to be.)
Reported on Movable Type 4.2

I have had the same problem, i saw empty tags where the gamer score was supposed to be, just as i started using it. Did you get any new info on this or it's still not working for you?