Google senior product manager Dylan Casey offered some insight as to how the search giant determines if a real-time update is relevant. “How old was the account, how often do they post, were they often outlinking or inlinking, are they often pointing to the same URL?” He said that Google is trying to emphasize comprehensiveness by including non-Twitter providers such as MySpace and Identi.ca (but Google currently has less access to Facebook updates than Microsoft does, so that might not be his best selling point). However, Google plans to soon publish a standard way to publish directly into the Google indext using pubsubhubbub, he said.

Casey said perhaps the most complex project in real time is to determine when to trigger the appearance of real-time results in search results. “We have huge internal debates on: Is this a good answer to this question, or are we just creating a tool for low-quality content?” he said.

How Google, Yahoo and Microsoft Think About Real-Time Search – GigaOM