It's not so much creating a forum, as creating a templated forum as this one is responding to various options. The evaluate funcion is used to parse the templates allowing them to contain conditionals and site dependent variables. I don't believe this is possible in ASP.Net.
Don't get me wrong I like ASP.Net. I just think they both have their place.
As for PHP being more time consuming - I completely disagree!
:)
Oh and thanks for the welcome!