Civilians think Gmail IS email. I gave my landlord my email the other day, and she was like oh, isn't there supposed to be gmail at the end of it? I had a custom domain.
It always confuses the hell out of people when I give my email as "<companyname>@mydomain.foo". I've gotten responses from "oh do you work here?" to just confused looks. It's really just to help me with filters (and null-route things should the email get too much spam)
What was quite ironic for me is that I bought a ".mobi" domain name, because it was the only TLD that I was able to get so it can be $first_name + "." + $tld. - It seems that the .mobi TLD is more confusing than ever for people. I originally got it as a shorthand to my actual domain ( routing all emails to my primary domain )