Had a situation where I had a legacy website that I was attempting to convert to WIF and claims-based and when I ran the application, all I got was a white screen and the application just hung.
Not that familiar with the application but obviously it somehow hides errors from the user.
There was error logging but nothing in the logs.
I was completely baffled.
So I loaded IIS Manager and started looking at various controls e.g. ".NET Authorisation", ".NET Error Pages", "SSL Settings" etc. in some kind of hope that I would notice something that would give me a clue.
Then I clicked on "Default Document" and lo and behold it threw an exception because of an error in web.config.
This application has a huge web.config and in hand-crafting the WIF constructs I'd duplicated some sections.
So I did a "rinse and repeat" until IIS Manager showed me the default documents.
Makes sense - to get the default documents IIS Manager has to parse the web.config and throws exceptions if it can't.
Really neat trick to remember.
Of course. it would be cooler if VS actually did this for you!