Is it case-senstive? No seriously, check and check again. Are URLs Case Sensitive?
I spend an hour today debugging a possible problem only to notice that "SignOn" != "Signon"
If I had a nickel for everytime Case-Sensitivity or Case-Insensitivity bit me, I'd have like seven or eight bucks. Seriously.
Moral: Know if whatever you're working on cares about Case, and if it does, make a Post-It to remind you and stick it to your monitor.
Oops, there's another 5 cents. Omar says FlexWiki uses Case-Sensitive Urls so http://wiki.shahine.com/default.aspx/DasBlog.VersionHistory != http://wiki.shahine.com/default.aspx/dasblog.versionhistory
This page says URLs are Case Sensitive if the Web Server exposes the underlying sensitivity of the OS and File System. This guy says yes, also but reminds us that the base domain ISN'T Case Sensitive (DNS doesn't care).
Of course, it gets even more fun when you remember that XHTML is Case-Sensitive (because XML is) while HTML 4.01 isn't. This sensitivity is exposed in the DOM for both.
Sigh. - sCotT hanSELMan