Why does it take so long for Visual Studio to start my web app in debug mode?
Check your Symbol Server
If you have a symbol server set up, and have the following environment variable '_NT_SYMBOL_PATH', your debugger may be retrieving symbols from a slow store. After some experiments (like uninstalling and reinstalling VS addins, etc.), I removed the _NT_SYMBOL_PATH variable from my system and voila! attaching the debugger is fast again.
Some analysis required here. My symbol path is quite long.
SRV*C:\data\symbols\OsSymbols *http://msdl.microsoft.com/download/symbols; c:\data\symbols\ProductionSymbols; C:\Program Files\Microsoft Visual Studio .Net 2003\SDK\v1.1\symbols;C:\winnt\system32
I thought to slowly remove stuff in the path until performance returned. It appears that VS caches the symbol path however (blah), making the investigation slow. I am suspicious of the microsoft web address.
It appears that removing the microsoft web address has fixed the problem. It's not really necessary to check for those symbols over and over again anyway. So I have removed it from the _NT_SYMBOL_PATH variable and I will put it back when I need it.