The offering is through a limited number of partners and it looks like YouTube wants to make this more widely available. The limited rollout is for obvious reasons (as in this thing might be buggy so keep it contained).
From the YouTube blog we read
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. For the purpose of the trial, this offering will only be available today and tomorrow. Based on the results of this initial test, we’ll evaluate rolling out the platform more broadly to our partners worldwide.
The limited rollout will be with partners Howcast, NextNewNetworks, Rocketboom and Young Hollywood. Check out YouTube’s version of TV Guide to see when you can sneak a peek.