I'm in a similar boat with my main email account. I also have a regular Gmail account, but my main email is my personal domain, which is set up with Google Apps. If something ever happened to Google, I could switch my MX record to point somewhere else, and keep using the same address. I use Google Calendar for family stuff, so it wouldn't be the end of the world if that were lost. My main calendar is through work, which uses Outlook and syncs to my iPhone.