One of my developer colleagues was working on a project this week and ran into a timeout problem while working on building some crazy web part. His web part was fine, but "suddenly" an unrelated site became very slow and frequently timed out with this error:
[HttpException (0x80004005): Request timed out.]
I logged in and saw that several other sites were just fine. I suspected that there were some hidden web parts on the page and using the trusty ?contents=1 debug technique, I did in fact find 11 web parts on the page, only two of which were visible. Even better (from a let’s-hope-I-find-something-ugly-here-that-I-can-fix perspective), three of those closed web parts had a name of "Error".
I deleted those web parts (which itself took a surprisingly long time) and that solved the problem. For today 🙂