Arduino Ethernet and Uno R3 as a firewall Is there a way to program the Ethernet Shield and Uno R3 to act as a firewall without using a huge chunk of the allowed bytes on the R3?  I plan on using a DC adapter to plug the R3 into a wall, and use the mini-SD card to keep logs while having the ethernet shield plugged into my router.

I know that it is possible to program it to do this but I want to know if there is a simple modification I can make to the web-client library or if I should use the web-server library and modify that?
As an entry level board, I wouldn't suggest trying this on the R3. You can do it to an extent on the Yun which comes with both a network port and wifi. 

Now that said, your internet speed will be severely hampered by the lack of resources on the yun. In which case, you might want to steer closer to the Intel Edison, which you can use with the arduino IDE. It is considerably more powerful.