I use Gmail as my primary email service and also like the other personalized Google services (Reader, Docs, Spreadsheets, etc.), but never really used Google Calendar much because I haven't found a simple solution to access it with my mobile devices. I just read on the jkOnTheRun blog that Google Calendar for Mobile has arrived. If you visit the Official Google Blog you will see that all you need to do is go to calendar.google.com from your mobile phone to see your agenda of upcoming events with details like date, time, location, description, and guest list. There is also the ability to add events to your calendar. Now I just need to get my hosted Exchange calendar in sync with my Google calendar and I'll be all set on my mobile devices.