You can easily get invite for Google plus. For those who want to ignore the +1 button, you can go ahead and do so. But when Google plus go main stream, you will have a heck of a time trying to catch up with the early adopters.

You can certainly get some benefits from the +1 button. People claimed that Google will use this as one of the social metrics to rank your site in the SERP. There was one case study in particular (either by Mashable or Technorati) indicated this very early on.

Others had also use the +1 button to draw more traffic to their sites. I can't find anything that will harm the site by using the +1 button early on.