A number of years ago I looked into which is more readable, this_name or ThisName. The descriptions people had about their perceptions indicate that the font has a lot to do with why this_name is unreadable to some. That is, the underbar is too faint or too low. In testing comprehension and reaction times, ThisName is the worst in this meaning of readability.

In terms of maintainability, simply having a convention is the important part. Comprehension and memory of the human reader is largely case-insensitive and delimiter-insensitive. Larry might argue that the programming language should match our perceptions on this issue. Hey, it worked for Pascal.