I'll go for 2x1Mbps anytime and hook them up on a load balancer. Why?

1. Can handle more session. Good for P2P softwares.
2. Redundancy. 1 down, there's one more. You're a heavy user so you'll need that.
3. Lower cost in the long run.

You will need a software like Free Download Manager or something else that offers multiple connection to a single host to download a single file in order to utilise a Load Balancer's capability... if you're using IE's own download software, it'll only utilise 1 line because it's only one connection to the host. As for me, i don't think i'll need a 2Mbps line for surfing and online games, it's an overkill. I'd rather have dual lines for redundancy reasons.