Ditto. BU is not selective. In the ASPH's 2008 Annual Data Report, BU has one of the higher acceptance rates.
http://www.asph.org/UserFiles/2008 Data Report.pdf
I suppose you still need to take those acceptance stats with a grain of salt though, bc they lump together applications for all concentrations, and I believe they also include applications for doctoral programs in those stats along with masters degrees.
As for applying for the spring, they say there's less opportunity for being awarded funding when you apply for spring enrollment (this goes for when you're applying to grad school in general, not just for MPH degrees or to BU). So I don't know if you'd still get offered any merit award along with your acceptance if you apply for the spring.