It's OK! You can be different PoR ;)
Although perhaps not that different: /Provider/Style/URI [w3.org] :P
I'll go for a compromise: if you have full control over sites and servers you work with, and understand how to combat any potential issues, then use whatever case you feel most comfortable with. Unfortunately, a lot of (most?) sites have either technical or editorial limitations, and that makes lower-case filenames the safest choice.
As for display URLs - I know I've copied and pasted a few in mixed case that led to 404s ;)
[edited by: Receptional_Andy at 7:10 pm (utc) on May 16, 2008]