Finally, the people at Google have realized that this is just an impractical solution to get invites to your friends. They grant you 150 invites, but realistically who wants to sit there and enter 150 different email addresses, and furthermore, who even knows all of their friends email addresses off the top of their head?
Enter the invite link. As of now when you click on the “invite people” button on the right side of the screen you can invite friends by email, or you can share your registration link with them. They still limit you to 150 invites because they don’t want Google Plus to become flooded with people, but at least it will help to actually get people you care about on to Google Plus.
Users can now just put a status on their Facebook wall and let their friends come to Google+. Hopefully, this will make Google+ a more active place.
Source : Google Plus Blog