A bit ago I posted about using Google Calendar in libraries. Many of the same principles apply to the question of how to have online calendars automatically add our trips when we make online reservations or add links to our receipts from online purchases. Imagine how handy it will be to check out from a hardware store online and click a link that will add a summary to your calendar of your purchases.
Even better will be the day when you can make in-store purchases and have the summary easily added to your calendar. Need to know when you bought that new computer (and when it's warranty expires)? Just click a link in your email receipt and away you go. It also is the answer to the calendar feature to kill for and it is available as soon as the travel sites add it.