OK, so this is embarrassingly mundane, but I just ordered a supermarket delivery online a delivery from Waitrose (I live in the UK, and it's an excellent if wallet-stretching store). And this time, interestingly, when my confirmation email arrived it came in the form of a Google calendar invite:

Title: Ocado delivery
When: Mon 12 Feb 12:00 – 13:00 (1 hr) (GMT)
Where: [my address] (map)
more details »

Going? Yes – No – Maybe


   Your Agenda for Mon 12 Feb 2007
   No earlier events
   12:00 Ocado delivery
   19:30 Ben for dinner
view my calendar »

I just click YES I'm going (to my own house, of course), and it neatly adds itself to my Google calendar. This is very nice. I don't know how Ocado do this, but I suppose they won't be the only ones now sending Gcal formated data in their emails.