I’m a Gmail addict. We run our company email on it. All my personal mail has been based on it for years. Lately, I got annoyed that whenever clicking a mailto: link anywhere on the Web, Apple Mail launched.
Now, Apple Mail likely is the worst email client ever written and – frankly – using Gmail with anything else than the Web based interface is just plain stupid from a productivity standpoint, so I really had to force my Mac to open mailto: links in Google Chrome.