I have been playing around with boids trying to figure out how to use collision objects and have come up with this example file. The orange land based Boids are attracted to the charcoal sphere which moves around the scene. When they encounter the green cubes they try to go around them. I have the look ahead set very high with a value of 100 seconds into the future. I found that if you do not set this value high enough boids will go through the cubes sometimes. The Particle Friction and Particle Damping, (under the Physics context) for each cube, affect how the Boids bounce off the cubes.
boid_attractor_deflector.blend (369 KB)