Better than boycotting GoDaddy (google bomb Namecheap)
Here is an even better way to hit them in the bottom line...
Add this somewhere in your webpage (you can just stick it somewhere in the footer)
<a href="http://www.namecheap.com">Domain Registration</a>
GoDaddy is #1 in google for "Domain Registration", but if enough people link to this (it doesn't take much) they will be nocked out of the coveted top spot. This will be a huge dent in their revenue stream.
This is referred to as a "google bomb" and it works by the fact that search ranking is based upon the the weight of the links pointed to a page. The name of the link helps them correlate the search terms that match with the link.
Namecheap was chosen as they have a high ranking (so they have a good chance at popping to the top) and has been vocal in being anti-SOPA. You can use the coupon code "SOPASucks" to get a discount there too.
I just added it to two of my sites - editthis.info and cueflash.com (both with a page rank of 5). That will hit them in the SEOs.