That is quite the name, but it works pretty much as advertised. I have been doing a lot of Regexing lately to parse t-sql code that people input into my latest intranet application. I figured I could share my regex pattern between the server component and the client validation control, but quickly found out a few things.
So with a little Googling I came accross ConceptDevelopment.NET's InsensitiveRegularExpressionValidator. I copy/pasted the source code into my project and had it almost working pretty quickly. Almost working because I got an exception that told me my ValidationExpression could not be null. Well I was setting my ValidationExpression in the page load event so I knew this wasn't true.
Thankfully I've read Nikhil Kothari's book ASP.Net Server Controls which helped me quickly spot the problem. The ValidationExpression was being stored in a local variable which meant it would be empty on the post back since I was only setting it the first time the page was loaded. Cool. I simply changed it to be stored in the ViewState and everything started working perfectly.
Overall this is a very cool control even if it is insensitive :)