Say you have a linux box with 3 network cards running a router distro. If you have one card hooked into the uplink port of a switch, then the other two cards hooked into different broadband connections (or different throttled LAN connections, as would be this case), can you get the two cards to load balance? IE. can you get them to equally share the internet activity so that you will get increased throughput? I think there should be a way (you can do it with commercially available routers) but what program/distro would you use? Thanks!

-G

Yes you can. Take a look at this howto:
http://lartc.org/howto/lartc.rpdb.multiple-links.html

You need to use the iproute command:

http://www.linuxgrill.com/iproute2-toc.html

Some people use zebra