I agree that G+ is going to have its moment in the not too distant future, as Facebook is getting more and more full of spam and making it hard to protect our privacy.
IMHO, G+ is more like Facebook than LinkedIn, even though for now, the G+ crowd is more technical and more B2B than FB.
Here is a blog I wrote on the G+ & FB topic to share my opinion :-).
In summary, it seems that instead of going more niche, which I see as the future, most platforms try to be everything. This won't work in the long run, for many reasons (see blog). Unfortunately, LinkedIn seems to be on this ill-chosen path also. I am sure you heard that 13-year-olds will soon be allowed to share content with their friends on the platform (argh!). It has been the best B2B platform for marketing so far.