One of the important growth driving factors were GoDaddy's Super Bowl 2005 ads, according to Netcraft. Their controversial ads gave them lots of free publicity:
In the 12 months since the Super Bowl commercial, Go Daddy has added 523,825 active sites, a growth rate of 136 percent compared to the year before. The simple fact that GoDaddy caused some controversy in the Super Bowl advertising scene provided the firm with some "free" public exposure. Netcraft quoted broadcast monitoring firm MultiVision, which estimated that the Super Bowl controversy supplied Go Daddy with the equivalent of $11.7 million in free publicity.More info over here.