Google is now gone a step further by allowing those same hashtags to be used when searching in Google. Simply type in “#keyword” for the hashtags you want to search:
The search results aren’t just limited to things of been shared on Google+. It also includes things such as Tumbler, some Twitter (as seen on the #Emmys search screenshot) as well as any kind of blog posts, new stories pages that are also utilizing the same hashtag
As for privacy, you can see any Google+ posts that are either public or the been shared with you personally, so you will need to be signed into your Google account if you want to see results that have been shared with you personally that might not be public.
Here's how Google engineer Zaheed Sabur explained it in a Google+ post:
So far, Google is rolling out the hashtag search was users in both the United States and in Canada, with the results. On both Google.com and Google.ca
- When you search on Google for a hashtag, say [#AmericasCup] or [#WaterfallWednesday], a set of relevant Google+ posts may appear to the right of regular results.
- You’ll only be able to see posts that have been shared publicly or shared with you.
- If you click on any of these posts you'll go to Google+, where you'll see the full set of relevant posts.
- You'll also see links to search for these hashtags on other social sites.
source : http://searchenginewatch.com/