Given the popularity of Twitter and Facebook competitions the question many compers are asking is whether Google+ will become another hotbed of giveaways. At the moment that appears unlikely, but some siteowners have already started to hedge their bets and utilise the Google+ button in the competitions.
This is a potentially risky move!
In their policy for the +1 button, Google state that "publishers should not promote prizes, monies, or monetary equivalents in exchange for +1 Button clicks".
If Google use the +1 button as a metric for SERPS then any site breaching policy may well find themselves on the naughty step. If your business relies on traffic from Google to function then gaming the +1 button for prize draw entries is not an advisable strategy.
In November 2011, Google opened up Google+ to brands. However, it does seem that they won't be allowing promotions and competitions. According to their terms "You may not run contests, sweepstakes, offers, coupons or other such promotions (?Promotion?) directly on your Google+ Page" (Google+ Contest Policy, The Sociable).