You've done a lot to increase his reputation. Look, you just said that the web server he wrote was good enough for your production work and that you believe other web servers to be inferior.
By mentioning Mongrel you increase the visibility and reputation of Mongrel, which increases his visibility and reputation. Now, when he introduces himself to someone he can say, "I wrote mongrel." And they will say, "cool!" instead of "what's that and why should I care?"
And assuming that he did, it was only after Zed Shaw wrote this post.
I only found out Mongrel was written by Zed Shaw when I read his now infamous rant about Rails and its community. (I'm not that a big Rails guy, but I did use it for a project).
Says something, no?
A license structured as "acknowledge your use or you will be sued," with penalties specified, as opposed to "please acknowledge your use" might have a different effect. I really have no idea.
Kent Beck's post from last month came to mind.
http://www.threeriversinstitute.org/blog/?p=231