The reason both Twitter and Google+ are struggling to grow their user base, IMO is because many folks I have talked to - find both products difficult to understand and use. Surprisingly most normal folks don't really get what "follow" means, and the slightly arcane terminology of twitter. The learning curve is a bit steep - and most users sign up, hang around for a while, don't really invest in discovering and following the right people, and soon just give up and never come back. The same is true for G+ - as in both cases your experience is defined by who you follow. Facebook got this right - as the simple concept of a "Friend" request translates perfectly to the real-world analog of making friends. While Follow is an abstract, invented concept with no real-world analog. That together with the torrent of noise and information on Twitter, and no good tools to filter and manage the feed efficiently, make Twitter a tough product to use even for experienced users. I personally love Tweetdeck - and have managed to tame the newsfeed with lists etc - but it is still tiresome and inefficient.