New report from Technavio (sorry, you need to pay) highlights the growth in the WAF market.  

Summary: "As more applications are being added to Web, the need for better security management arises. Hence, the Web Application Firewall (WAF) market is growing at a rapid rate."

Key highlights:

• The market for Web Application Firewall is forecast to reach $437.6 million in 2013 from $181.8 million in 2009; thus, growing at a CAGR of 24.6 percent over the same period.
• North America and Europe will see 24 percent CAGR through 2013 while APAC will grow at a 27 percent rate.
• Market size in 2010 $234M worldwide.