I'm pretty sure it's linked to your origin or xbox account, so there's probably no crossover between the two.
It's linked to your Origin account, which is why
there's crossover between PC and Xbox - even if you're on 360 EA makes you have one to play. It should cross over with PS3 as well.
Well I hope so becuase then I can basically just use multiplayer on the PS3 which I do better on and reap the benefits on both the PC version which I can carry over stuff from both ME and ME 2 on and the PS3 version.