We only know that people will TRY to game +1 - or any new feature for that matter. If they've got any street smarts, Google engineers will use a degree of confidence metric before they apply anything to the ranking algo. In fact, it should require other corroborating or reinforcing signals and never be applied on its own, IMO.
Of course, anyone with street smarts would also have realized there would be attempts to game Google Suggest, but that hasn't shown significant immunity to games. It is getting harder, but it is still happening.