Much harder if you use Google Apps for your domain. Many devices get ties to these Google accounts and severe breakage happens if you move those addresses or downgrade them
Harder, but not impossible. It's interesting the range of reasons people come up with (what about spam! everyone else is using Gmail!) not to do this.
Not always the best option for everyone (obviously).
your link to hacker news at the bottom of the article doesn't link to hacker news.