Here's a small web application you may find useful:
What HTTP Response Headers - WhatHeaders.com
I made it this past Saturday, when the rain outside wouldn't stop. Basically, when any HTTP client makes a request to this URL, the request headers are reported back. It's useful when you are working with any kind of "black box" HTTP client you want to understand better. I made it to easily get this information for mobile phones and handheld devices, whose behavior is often mysterious and aggressively undocumented.
As a convenience, you can have the header info emailed to you (again, quite handy (har!) on mobile devices). Let me know what you think.