Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
OS X is fully capable of handling multiple networks at once seamlessly (using multiple WiFi cards).

Are you sure about that? How are you going to route the connections? You can't simply use two connections to speed up your internet access. While you can have multiple network connections, you have to set it up to route connections via address. When I was working we had systems with two ethernet connections, but one was for internal LAN and the other for external.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.