I've never done this and am not advocating it, but... what's to keep someone not staying on Disney property from getting on the resort monorail at MK?

We were there over NY, and the crowd waiting for the express monorail was down the ramp and going through a "rope" cue. Since we stayed at Poly, we could get on the resort monorail (line started about 1/2 down the ramp).

But no one asked to see a room key or anything. So (aside from honesty), what's to keep someone with a car in the MK lot from getting on the Resort line? IIRC, the resort line stops at TTC anyway.