That would have possibly been true before the Facebook acquisition, but once the sale went through, I got about 20-30 new requests from people that were on FB b

That would have possibly been true before the Facebook acquisition, but once the sale went through, I got about 20-30 new requests from people that were on FB but not Instagram, and I'm not even remotely popular. I can't say the FB to G+ conversion I saw (amongst non-techies) was as strong. You're also not accounting for the fact that Instagram is a mobile app with a single focus. I don't want to go into my G+ app and filter by photos and hope to get the same quickly-see-what-my-friends-are-up-to experience I can with Instagram, just like I wouldn't post those kinds of photos to G+ to begin with. It's a very informal platform and I don't think G+ comes close to replicating that experience.