Their pricing system is way open to abuse (Score 2)

From their pricing page:

...Curl Corporation's usage-based software compiles information from end-user plug-ins that encounter Curl content. Included in this information is the number of characters of Curl content that are executed by the plug-ins. Curl Corporation's fees are derived from the total volume of Curl content executed by the plug-ins together with a price per one billion characters as determined by the customer's annual minimum fee commitment.

Ok, let's say that some website that I don't like uses CURL. What will stop me from hacking up something that will keep reloading a certain page and causing them to be charged by CURL corp hundreds (if not thousands) of time. Even better, what if a CURL employee visits a site with CURL, s/he would be generating revenue for CURL corp. It can get more interesting. What if CURL corp. hires people all over the world (where US law does not apply, and FBI can't investigate) just to visit their customers' web-pages tens of times a day. The victim would not even know!

Just my $.02