  We study the classifying space B Diff(M) of the diffeomorphism group of a
connected, compact, orientable 3-manifold M. In the case that M is reducible we
build a contractible space parametrising the systems of reducing spheres. We
use this to prove that if M has non-empty boundary, then B Diff(M rel boundary)
has the homotopy type of a finite CW complex. This was conjectured by
Kontsevich and appears on the Kirby problem list as Problem 3.48. As a
consequence, we are able to show that for every compact, orientable 3-manifold
M, B Diff(M) has finite type.
