G+ is Google's centralized system for single-sign-on and account profiles. It used to be confusingly distributed over multiple services, now it is unified. Oh, and it has a news feed associated on it at plus.google.com that you can totally ignore if you want.
Some of the reactions to this are way over the top. I guess I'm burning karma points by posting this, but it is an annoying trend.
The defense that you can only half-participate in g+ is not much of a defense because 1) people may not want to support changes of that sort with their patronage lest it continue as a trend, and/or 2) the thing being objected to was a forced escalation of participation - why would a user assume this would be the last and that half-participation in g+ will remain an option?