That is, don't use Cassini in your development environment if you aren't planning to use it in production.  For example, my customer is running IIS on their server.  Why shouldn't I do the same?  With what I have seen with Cassini, there is no reason.

Cassini is great, but there are noticeable differences between it and IIS.  I am using a third party menu that performs poorly through Cassini, but works fine on IIS.  Others have documented differences in behavior with Cassini.  Scott Lilly  describes a couple of scenarios where Cassini behaves differently than IIS.  Other examples can be found here and here.

So, if you are running VS 2008, your website will be executed on Cassini by default.  How do you change it?  From, the Website Property Pages dialog, under Start Options...  Select "Use custom server" and enter the URL for your virtual directory (assuming you know how to create a virtual).