Yeah, it strikes me as weird that it would be a problem with the graphics card, especially since it appears to be intermittent (since it works every five times you try it). And it couldn't hurt to search around/start a thread at MacRumors while you're waiting for the other responses, eh?

The 90 days is for technical support, but you get a full year of repairs coverage -- so if you need repairs, you should be all set. And even though the 90 days is up, if you haven't called technical support yet, I think you get at least one complimentary support call. It's worth a shot, anyways -- if not to AppleCare, then to an Apple Store or general Apple Inc. support line. Good luck!

Take care,
Sojourn