Selected answers from the Dumb SEO Questions Facebook & G+ community.
Suraj Gadage: +Policy Advisor It depends on the web servers. Some web servers do not treat URLs as being case sensitive. This means that your visitors won`t see an error page if they follow a link that accidentally points to a file /TestPage.html but actual page is /testpage/html. You need to do the same test for your website and see how this is handled. If you get an error message it means your web server is case sensitive. How does this impact on SEO?If your web server is case sensitive then Google can treat the same page as two different URLs. Also if someone has linked to your webpage as above mentioned example then they will get a 404 error and link equity will be passed to a 404 page.How to fix this?Add a case-insensitive mod_rewrite redirect in your htaccess file.Hope this helps!
Federico Sasso: Short answer: yes, and yes.Google and other search engines do respect the specs and treat URLs that differ in casing only as separate pages. If the web server uses a case-insensitive file systems (e.g. MS IIS) a simple error in casing in a link would lead to an internal duplicate content issue.In case of case-insensitive web server, best practice is always to use a self referring canonical tag for the pages you want to be indexed, other than always checking your internal links (which you`d also do in case of a case-sensitive web server).
Are URLs Case Sensitive and Does It Matter for SEO? 
