The large number of September 1st rentals is a result of the college population moving back to Boston and getting ready to start the new academic year. I cannot think of another large metropolitan area that is so significantly influenced by the local college population. Within the metropolitan area there are more than 100 colleges and universities, and according to Wikipedia there are more than 250,000 college students in Boston and Cambridge alone. If that figure is correct then that means college students comprise more than 35% of the population.
Despite the fact that parking will soon become near impossible with tens of thousands of college students (many for the first time) moving into Boston, I look forward to their return. The soul of Boston is tied to the students who come here and make it their home (at least for awhile). Its partly why Boston remains one of the youngest cities in the US despite the Northeast having one of the oldest populations. The students and those who stay after graduating shape and influence this city as much today as the immigrants who are a part of this city's history or the large employers who have helped draw people here with good jobs.