If you are interested in strategically using hash tags on Google+ you'll be interested to know the following.
A hash tag search used to return results from hash tags added in comments on posts, and to shares of posts.
Now they do not.
An older change is that when has tags were introduced they used to remain clickable.
For some time now hash tags after a certain age cease to be a "clickable" search link. That's the case for the comment hash tag pictured right.
Previously I have added a hash tag comment to group related content together. That comment would have returned "other people's content" in search results along with any posts where the hash tag was added by to post author directly to the post.
Now an #UpCologne search will only return "primary" hash tags not secondary, added to comments hash tags.
Also note that hash tags added to reshares count as secondary tags and are not returned in search either. Which is why this post doesn't show in a search on the hash tag that was added to the post of the share.
Hash tags are still very useful and also as search hash been able to be triggered by hash tag with is "past it's sell by date" new searches, fresh usage of the hash tag will still return primary results.
So hash tags are still, for example, better than twitter's hash tag offering.
So what do you need to do?
Just remember that it's primary tagging that is still as effective as ever, it's just that now you can't use tags to "help" group other people's content together. It's up to the post author to add them.
p.s. This is an "add on" post to the Google+ Course. If you would like to read more go to the course index.