At this point in my life, a solid 70% of everything I've ever said resides on Google's servers somewhere. If the company were to ever close its doors, those words would be lost to history. But that's about to change. Google's rolling out the ability to easily download a copy of your Gmail and Calendar data, so you can migrate it to another service when the unthinkable - or the inevitable - happens.
Gmail data will be provided in the MBOX format, while Calendar will shoot out your schedule as an iCalendar file. You can start exporting right away, but for the time being, most people will only have the option to export their calendars. Google will roll out the ability to download Gmail messages over the coming month.