I get pestered with messages from Google on various services asking for my phone, merging/creating accounts, joining Google+, etc. Often the UI is so that for an average user it's not clear how to opt-out from it. Undoubtedly on purpose.

Each time you want to sign out of Google, there's an ever present, huge bright button - "Join Google+". I suppose more than one person clicked it by accident or out of frustration :) On rare occasions when I use Chrome, it never forgets to remind me how I'm missing out and should totally sign-in to Chrome.

Staying relevant is hard work :)