Google have made changes to their desktop search results and will now start displaying Tweets in all English language searches.
Tweets have featured in Google search results on mobile platforms since May, so it was always a probability that we would see this feature being implemented on their desktop versions also.
The Tweets will show up in the Google search carousal even if the user has not signed up to Twitter, or is currently logged out.
Google say they are still in the process of growing and evolving this feature; and just like how they are constantly tweaking the algorithm for regular search results, they are looking to improve the relevancy and ranking of these new Twitter results.
In terms of SEO importance, Twitter just became all the more relevant.