With a one-year-old and two pets, I use my Nexus One’s camera almost daily. I created my Google+ account many months ago. I almost never use the Google+ App on my phone. However, photos I took starting on December 2 began to show up in my Google+ “notification area” when signed into Gmail. Now, they’re not shared by default, so there’s no “real” harm done in the near term.
Photos from November 27 were not uploaded. I conclude that something happened between those two dates to re-enable Instant Upload.
Quick fix: Google+ App : Menu softkey : Settings : Uncheck the Instant Upload checkbox.
It is entirely possible that a regular App update tried to warn me about this. However, to me, this is a significant change that should have warranted an additional effort to notify me about it.