I hang around on LinkedIN. With Google+ in its invite-only "field trial" stage and people writing blog posts raving about it, LI's Questions have been inundated (or maybe people just aren't reading before posting, how unusual) with "Is Google+ a Facebook killer?" style questions.
Same question all over teh interwebz by anyone who cares to write a blog post about it.
Other similar ones that pop up are "Is [this shiny new Blackberry|Android thing] an iPhone killer"?
It's kind of a stupid viewpoint to take. Unless of course you're a marketer and you're desperately trying to make people believe that THERE CAN BE ONLY ONE and your thing is it.
No.