It gets even more confusing if you have a Google Apps for Domains. I've had andrew@ducker.org.uk for my Google ID for a fair while before I got them to manage

It gets even more confusing if you have a Google Apps for Domains. I've had andrew@ducker.org.uk for my Google ID for a fair while before I got them to manage the email/calendar/etc. for ducker.org.uk - at which point calendaring got a bit complex for a few days - and it took me a while to get sharing set up again properly. Some of this stuff really doesn't seem that well thought out, to be honest.