I have an opinion on this and someone feel free to correct me or offer another perspective, but, here we go
:
First, no, I don’t believe Google search is case-sensitive, and I doubt this is affecting Adsense ads, but I could be wrong on that point.
Second, using mixed case in URLs is horrible for users and accessibility, cause on Linux servers, unless they get the case exactly right, they’re going to get a 404 (or referral to the error page in our case). I recently converted a site that was originally deployed like this via FrontPage and on the ’nix server, it was a mess to say the least, so I followed recommendations I’ve gotten from many SEO experts (and from using WordPress, which is where the majority of the alias cleaning concepts implemented here came from) and made them all lower-case, replaced spaces with a dash (-), etc. But to prevent breaking the mixed case links, I implemented one change to the MODx friendly URL rewrite rule to help manage the case-sensitivity:
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA,NC]
Notice the NC at the end, which indicates to mod_rewrite to ignore the case of the request.
Again, just my perspective on this; I’m just hoping I can have the option to apply the alias cleaning rules even if I don’t use automatic aliases?