I’ve been using Google Docs and Reader for a long time now. Reader is the only RSS aggregator that lets me whizz through hundreds of feeds fast enough to keep up to date and from various devices (tried feedburner and newsgator). Docs made it easy to share any document, presentation, todo list with a friend in 2 clicks, and now Docs and Reader have offline support (Google Gears) the worry about not having net access at any point is gone.
However, the subject of the post is Google Calendar, which has probably been the most useful app so far. I switched to using Google Calendar for all my calendar needs for several reasons:
1. Read/write access from any device at any time, including iPod Touch (fantastic support), or basic mobile phone
2. Subscribe to calendar in Apple iCal (or Outlook etc)
3. Automatic reminders via free SMS, email, popup and iCal alarm.
4. Upcoming events in Dashboard widget, and on my Google Homepage
The one limitation was that you had to visit google.com/calendar to add an item, but their intelligent new event creation made that easy (e.g. click new event, type “meet XYZ Tuesday 7pm at POSTCODE, hit enter it would automatically add the event, a reminder and a link to the map location).
However now Google have added CalDAV support, you can now add it as a CalDAV account in iCal for read/write access directly.