It is fashionable to slam Twitter on Google+ and regard it as superseded by Google+ but Twitter remains compelling, effective and easy to use. Its not quite the simple tool it used to be touted as but it does its job really well.
That said, Google+ does somethings better so its really a matter of using these tools for what you need to achieve and selecting the right one for the right job. I am looking forward to seeing what happens to Twitter’s active user-base when iOS5 rolls out next month to the public with Twitter integration. Revenue model or not, Twitter is fast becoming more of a phonebook that Facebook ever did or will.
As my habits stand, I don’t see myself being able to give up Twitter, Google+ or even Facebook without seriously compromising my online communications options. Of the 3, Twitter and Google+ are the two more important tools for me right now with Facebook a very close 3rd and purely because my friends and family are entrenched in Facebook and I can’t remember all the birthdays!