This a bug of VS 2005. The slowdown issue occurred when breakpoints were set in multiple source files in the same project that had the same short file names (for example: two default.aspx.cs files) and which were organized in a certain directory structure pattern on disk. The patch fixes this issue and should prevent the debugger from pausing when trying to load the web project’s assembly symbols in this case.
A patch exists here and there is also a relevant KB.
Περισσότερες πληροφορίες στο http://weblogs.asp.net/scottgu/archive/2007/08/21/public-hotfix-patch-available-for-vs-2005-f5-debugging-performance-issue-with-asp-net.aspx
