I tried, but gave up on Squid as I couldn't get it to work reliably with large downloads. See http://forum.pfsense.org/index.php/topic,21458.0.html
Here's a (quick & dirty) list of Rapidshare networks: http://www.uebi.net/howtos/rapidshare-networks/rs-networks-20090908.txt
I now set up an alias based on this list, and route Rapidshare traffic to qOthersDownL with the built in Pfsense traffic shaper.