After 3 months fom launching google plus now is open as an ggoogle services like Gmail, Docs rtc… all you need is a google account. No invitation need to login, you can straight create your profile there.
ie. Google + moved from trial to beta
Till now google plus got 25 million visitors as per comscore report
To Get started with your Google Plus
Go to http://plus.google.com
Click on Sign in, it ll ask you for your google account, if you have one log in with tha account or simply create a Fresh account, Start Google Plus instantly