I don't believe +Mike Elgan
has completely understood all the benefits you gain from hash tags.
Hash tags is a brilliant way to give your post; keyword tags, meaning you can search posts; and the tags will promote your post upon your set tags. This then comes to the problem, +Mike Elgan
mentioned, of self promotion.. Google will most likely favor your post in searches; if your hash tag corresponds to the search keywords.. This would be a problem to solve, as people can hash tag as much as they like..
I believe, +Mike Elgan
also missed the point of being able to trend your post, this means your post will link directly to the Google+ search engine. I find this tool very useful, as I can directly follow a trend. I can then read more upon recent news and similar posts in the click of a button... If people use this tool well it would significantly advance user experience when using Google+...
The only thing I suggest Google do to stop spammers self promoting their material; would be to limit the amount of hash tags per post so you don't have mass spam problems...
Does it matter if it doesn't work? Google+ is still in beta, meaning things will go wrong... and because Google actually listen to the users they would revert back if there was a significant drawback to having a new feature.