Now when you search Google, a nice number of search filters have been removed, including the discussions filter. The number of filters or vertical options have been drastically reduced. Here is an example.

But if you look at an article from six months ago, the options for that search were much more vast.

Now we have web, images, shopping, maps, news, videos, books, flights and applications. We are now missing places (which is maps I guess), blogs, discussions, recipes, and patents.

All Google Testing also notes that the order of the filter options have changes based on your query. Interesting.

For some, the removal of these additional filters is very upsetting. A Google Web Search Help thread has one searcher who said "very annoying as I rely on this function a lot."

Forum discussion at Google Web Search Help.

Update: Here is a response from a Google spokesperson: