Shift-A --> Force Field --> Boid produces a force field of type "Boid"... which has no appropriate interface and does nothing. There are no docs explaining what it might do beyond a copy-and-pasted bit of copy from a textbook explaining the basic Boids principle.
This appears to be a vestigial feature that ought to be removed. (If I'm wrong, enlighten me and I'll write some updated docs myself)
Note that this is completely separate from the Particles --> Physics --> Boid feature, which works as advertised.