It seems Google+ is now looking for feedback on how it can make the service better for its users. In short, Google+ is now seeking beta testers. The announcement – which of course came through Google+ – states that those who do sign up to be part of the beta program will not only gain access to new features, but will also be able to chat with the Google+ product team, as well as other beta testers.
As for the caveats, there are some. Firstly, Google+ only seems to want those who are "active" posters on Google+. The announcement does not specifically explain what constitutes as being active, so this may be more of variable. Secondly, those who want to join the beta experience are expected to be "motivated to learn" about Google+ and equally, be motivated to provide feedback via product discussions. The last caveat, which is more of an extension of the second, is that Google+ is only looking for those who are willing to provide "high level feedback" – which presumably means more detailed and thorough feedback then simply ticking a 'like' or 'dislike' check box on a form or survey.
Other than that, there does not seem to be any other major hurdles in becoming a Google+ beta tester. As is usually the case with such things though, it is likely that Google+ is looking for a select number of users – or at least a maximum number. While there was no mention of that number in the announcement, those who do want to take part should probably sign up sooner rather than later. Speaking of which, if you do want to sign up to be a beta tester, there is a short application form that needs to be filled out. One which mainly focuses on an individual's use of Google+, such as why you use the service, how long you have used the service for, and why you want to be part of the beta. As well as some other testing-relevant aspects that will likely improve an applicant's chance of selection, such as how many and what languages you speak. The link below will take you directly through to the form which needs to be completed and submitted.