Google Calendars

E-mail and e-mail related calendar tools date back to before the HTML graphic interface to computers. One of the more widely used multiple interface calendar tools is Google calendar. The feature sets continue to grow and improve. Here is some of it:
Sync Calendar with a phone or tablet
Sync problems with the Google Calendar app
Change your settings
Share your calendar with someone
Get started with Google Calendar
Invite people to your event
Notifications
Android app (4.1+)
iPhone app
Other app
Create an event
Edit or delete an event
Invite people to your event
Create & subscribe to new calendars
Print your calendar
How to search in Google Calendar
Sync with your phone, tablet, or computer
Export your calendar
Import events to Google Calendar
Fix problems importing
Event & notification settings
Calendar settings
Google Tasks
Help Forum Interface

As you can tell there is a lot of functionality, and learning to manage it all across the numerous e-mail and calendar sync'ed interfaces seems excessive. SO you probably just go with the interface chosen at your work place, or on your pet project, But then again someone had to decide which one to use. If you use Google, or one like it and have an opinion, We would like to hear about it. How does it compare? Does it interface well with any others you have to use? Is one system any more buggy than another?

Teamup.com is a Free scheduling and room reserve system for Teams (or at least has a free level)

Teamup.com is our first calendar for discussion. If you have tried it please comment here on your opinion?