Stacy G - I am starting to see an uptick in comments, +1 activity and definitely a viral increase in people within my circle (over 300 for my marketing tools page now).
All that has an impact on your Google search results so it is worth it. I don't believe you can track uplift in traffic in the organic search results related to your circle yet, but I do see referrals directly from my posts.
Like any social media outlet, it takes time to build the presence and see the impact. But Google is putting a lot behind this and I really don't feel like you should sit on the sidelines. There is nothing worse than being in catch-up mode later.
Here is my G+ page:
I am following everyone on this trail either as Diane Seltzer, Small Business Marketing Tools or BoaterLifeOnline (depending on the relevance). Thanks!