<Rant>
I am in the process of playing around with the routing library for my current project, and I am playing around with using routing for web forms. I was running in IIS7 Classic mode (Don't ask why integrated works fine but I was seeing how this would work in IIS6 by testing with classic mode), I added a wild card mapping so that all requests would run through the asp.net pipeline and it just would not work.
I litterally banged my head against the wall for hours and no matter what I did the requests were not running through the pipeline. My dev machine is running vista 64bit and I never even though of this, when I was mapping the wildcard I was mapping to the 32bit framework. Argh, I luckily found the option in IIS to enable 32 bit applications and this fixed all my problems.
A day of headache and a click to the solution, I love doing this sometimes :P
</Rant>