Yesterday, Google has completely removed the ability to use their discussion search filter. Earlier this year, Google removed the feature from their search filters but savvy searchers were able to access it via Chrome extension or by going to google.com/?tbm=dsc which would power the discussion filter.

Google completely disabled it so now you can no longer filter Google search results by discussion forums.

Many searchers are not happy with the disappearance of the feature.

Forum discussion at WebmasterWorld and Google Web Search Help.