Don't confuse your self - If you browse to http://www.whatismyip.com/ and hit F5 (refresh) you should see your IP change each time. This is because each time you hit F5 a new session is created and fired out the next available modem on port 80 in a Round_Robin fashion.
People uploading from you, say on a website you host will still be coming in via just one modem and will still be limited to that modems upload capability.
In order for you to make full use of both wan links you will need to use something that makes use of multiple session that can be fired out each modem e.g. peer to peer software like emule or uTorrent.
I tend to keep the traffic separate and send priority traffic out one interface and bulk out another this is the simplest form of traffic shaping. You could implement full traffic shaping but it is quite complicated to get right and can make it worse if you get it wrong - you might want to wait till 2 come out of Alpha before you try it.
What you have set up will make use of both WAN links.