Once the deck of destination cards runs out, you could start drawing two train cards from the deck every turn, and keeping them permanently. There's no hand limit.
If you're bored with Ticket to Ride, this is a great way to ensure you're never invited to play it again.
(12) Mon Sep 10 2012 11:54 Ticket to Grief:
Ticket to Ride comes with 30 destination cards. You can start out with three, and on your turn, you're allowed to draw three new cards and keep them all. This means you can very rapidly take almost all the destination cards for yourself. You would get a very large negative score, but prevent the other players from getting a good score or having anything to do in the endgame.