The City is compiling information about biking around Boston. The Boston Bikes map is a compilation of what the City has heard are the best (and worst) biking roads in the city. You can send your comments to the city using this survey.
Apparently you have to be an "advanced" cyclist to get much of anywhere in Allston and Brighton. I'm surprised to see Market St, Lincoln St, and North Harvard St in the middle tier of roads because of their steep grade, narrowness, and abysmal road conditions, respectively.
Unfortunately the map file is 14MB and I had to try a few times to download it from the City's website. You can see all of the A/B info by clicking on the image to the right.