According to the Boston Business Journal article: Google goggles Hub for major expansion, that the Boston area is one of four cities that Google is considering for a new Googleplex. Company representative have looked at more than 10 Boston/Cambridge locations in the past seven days.
The three other cities in the running aren't listed in the article but as far as Boston goes, Google wants 75,000 sq. feet of office space with an option to expand to over 200,000 sq. feet in the next 18 months.
The article goes on to mention that Google would hire up to 1,000 "mid-salary workers." The company already has a small sales office in Boston.