Here's a good definitive list of which events cause an ASP.NET AppDomain restart. These are important since and AppDomain restart will cause you to lose any inProc session you have for a given user.

Things like adding, modifying, deleting assemblies from the bin folder, changing source code files in app_code dir, changing web.config, etc.

ASP.NET Forums

Tips/Tricks from ScottGu about optimizing builds within VS2005 for Web Site & Application projects. Includes a discussion about which builds faster under which circumstances, and a list of things to look at for each type of project that can hinder the build times.

Web site projects:

• Dueling assembly references
• Keeping app_code small
• Enable on-demand compilation

Web application projects:

• Split large projects into multiple sub-projects
• Look at using Web Deployment projects