http://sched.org/ , a great web app , "twitter style".. can be the google-calendar killer ?

At first sight you only have a "daily view", no weekly view or monthly view. You also can't receive reminders (on mobile phone).
So, can it be the Google Calendar killer? The answer is: no. Not now.

Anyway, I agree that Google Calendar should allow to share events and/or calendars a little bit easier.

It's used for a different purpose so I wouldn't call it a Google Calendar killer. A cool app nonetheless.