Google+ users: Will you leave Facebook? If not, why?

Still in invite-only mode (I believe), Google+ is reported to have millions of users already, and the current plan is for it to go public at the end of July (I think).
If you have had a chance to use it, do you plan on migrating from Facebook once you can convince your Facebook people to come along, or is there something else that would keep you from leaving Facebook.

If you don’t plan on leaving Facebook and plan on using Google+ too, what purpose will each one serve?