Google+ analyzes what your post is about and auto-populates tags for you to amplify the reach of your public posts.
All I did was type my post above and it detected that I was talking about Twitter & Lead Generation so the post was automatically populated with those hash tags. I like how content is aligned with tags without cluttering up the actual post!
Check out my G+ post above at https://plus.google.com/106053321510794625997/posts/TmZeiobeuhq and click on the #Twitter or #LeadGeneration link that G+ populated automatically to see other posts about that topic on Google+