> Camel case is easier to type, and underscores are hard to type.
I'll grant it that, but in the context of programming, this does not seem to be a "pro". After all, don't we spend far more time reading code than we do writing code?
I'm old, but I'm still surprised at how I have to fight over my reluctance to do something in another language (such as Python) when I remember that it's conventionally camelCase...on the other hand, I try to use it as a personal advantage...I can immediately tell in a body of code what helper functions originated from me, as I'll habitually write them in underscore (though this probably annoys the shit out of anyone who then tries to read/use my code).
Conversely, my enthusiasm for using R jumped when I read Hadley Wickham's style guide and saw that he endorsed underscores (http://r-pkgs.had.co.nz/style.html)