I have seen a few a few Live events on Youtube like "Hope for Haiti Now" in January this year and President Obama's Address to Congress last year.
I was not unhappy watching both the events and I got what I wanted. There may have been more but above are the ones I remember.
But Youtube is about to change all that, in what seems to be a forerunner to an upcoming feature, it has entered into a new testing stage. Today and tomorrow, YouTube live streaming will be testing starting at 8:00 a.m. PT, we will begin a limited trial of a new live streaming platform in conjunction with four of our partners: Howcast, Next New Networks, Rocketboom and Young Hollywood. (You can try these and more from the above control panel)
This new platform integrates live streaming directly into YouTube channels; all broadcasters need is a webcam or external USB/FireWire camera. Included in the test is a “Live Comments” module which lets you engage with the broadcaster and the broader YouTube community." said Joshua Siegel, Product Manager, and Christopher Hamilton, Product Marketing Manager
YouTube Blog: Testing, testing...YouTube begins trial of new live streaming platform