In what is being widely viewed as a blow against Facebook, Google has announced a policy change (effective 11 November) permitting Google+ users' +1s, follows, shares, and other social activities to be used as "shared endorsements" on ads (name and G+ profile photo) subject to a number of important constraints (note that this particular link will not directly resolve unless you're logged into a Google+ account). Announcements of this change are already appearing to Google+ users through a variety of banners, emails, notifications, and other means.
At this time -- as I currently understand the program -- such endorsements will only appear on ads displayed on Google sites -- not third-party sites.
The scope of such endorsed ads' visibility will be limited by the scope of the original G+ user's social actions -- e.g. only to circles, or to broader audiences like public if the original actions were public.
Most importantly, G+ users can not only choose to completely opt-out of having their profile used for endorsement ads (via a setting at the page linked above), but users who already have restricted settings may already be defaulted to non-participation.
This opt-out control appears significantly broader than controls offered by Facebook (they allow opt-out from explicit ads, but apparently not from a different form of commercial endorsement postings) -- Google allows total opt-out.
Whether or not a given Google+ user may wish to participate in this program will be a personal decision, of course.
I have a quite large Google+ following, and nearly always post publicly -- so sharing is a very important part of what I find useful and attractive about Google+. That said, my personal decision (folks have already been asking me) is not to participate in this new program at this time, since I consider my social sharing activities to be more of "hey, you might find this interesting" posts rather than commercial endorsements per se (when I wish to make a commercial endorsement, I do so explicitly).
Other Google+ users are sure to have a wide range of their own views on this -- as the saying goes, your mileage may vary. I'm certain that many users will indeed choose to participate, and that's why having an explicit control as provided is such a great idea -- individual choice for the win!
In any case, it should be very interesting to see how this plays out over time. It's clear that social signals are of increasingly important significance in helping users navigate the enormous environs of the Web, and we're really very much still in the early stages of exploring the possibilities.