In development, our Asp.Net 4 website takes a fairly lengthy time to start after the project libraries are built
We do a fair amount of population of statics etc, but not enough to justify the length of time it takes the app to come up (probably 3-4 minutes)
We aren't building the website, just the libraries, and batch != true in the compilation element in the .config file.
I will try log some diagnostics, but any other pointers would be useful