Tech-centric people and those you expect to see on forums yes, the overwhleming and crushing majority use facebook though.
G+ isn't a Facebook alternative per se though. Facebook is more personal... Most people use it as an interface with people they know to some capacity, and honestly, it works really well from that perspective. G+ is a more universal social framework meant to be used as and if one pleases to use it.
For starters, you don't have to
really use it -- not unlike Twitter, where many simply retain an account for reading news and following other people / pages they interest them, you can simply watch what's going on (or not even that). And if you do post, you can choose how to share what you want -- in a discrete or open manner; or a combination, since it's designed with that in mind (and circles work quite well).
I'm not saying one is better than the other, but that they are made for two different purposes. Social doesn't work with everyone, which is why I understand maintaining a Facebook account can be a big deal for some. But a G+ account is not unlike a member card to a club that doesn't really expect you to participate in any specific way if you don't want to.
