There is, roughly speaking, a B+ average. (It's something a little more complicated than that, official info here: http://www.bu.edu/law/jd/curriculum/compregs.html#ArtIX
Of course the actual GPA doesn't matter so much. Employers seem mostly concerned with one's rank within the class. Rank is only determined at the end of each year. What kind of grades would you need to be to make the 1/3, .25, and .10 cuts? You can get an idea here:http://www.bu.edu/law/jd/registrar/grades/awards.html
(they just took down last years numbers, but they'll be out again soon for this year's 1Ls and 2Ls (3Ls get grades early so they can graduate).
The GPA cutoffs should be irrelevant to outsiders of course, because the difficulty of getting a certain GPA is a factor of rank in the first place (because the classes are curved). In other words - my favorite line: to be in the top x%, you have to do better than 1-x% of the other students. It's simple, circular logic, but most entering students believe they'll be near the top. Most are thus wrong.
As far as competition, every year will be different because there are all new students. I wouldn't say I've experienced any institutionalized competition, but maybe I've been sabatoged and I just don't know it. After all, shouldn't I
be in the top 10%?