I ran into a weird case when someone included a module I wrote twice. Once using all lower case, and once using camel case. This was on a mac, so the require worked in both cases, but the module ended up actually getting required twice -- and it caused some things to break.
I understand that this issue is a little sticky, as it matters whether you're on a case sensitive or insensitive file system as to what the behavior should be. But, node could take the stance that require is case-insensitive regardless.
We're not going to make changes to the module system unless it is a matter of life and death.
I'd recommend bring this up on the nodejs-dev mailing list. If a lot of people agree it's important to be case-insensitive, then I could probably be convinced, but it'd be best to keep that area of the code as stable as possible.