Me not being a lawyer doesn't make google less suspect for monopolistic practices. The US senate has been investigating it[1] and and new concerns are raised now[2]
http://www.washingtonpost.com/business/economy/google-faces-...
http://betanews.com/2012/01/10/googles-new-personalized-sear...
In any case, the one who should be worried is facebook, not twitter. It's also interesting to note how google is going at greater lengths to promote G+ than it did with any of its products before.