I'll offer you a 10$ to 5$ bet:

Take 10 migrated github repos at random (1) If they did not increase(2) the number of serious(3) contributors, I lose 10$. If they did, you lose 5$.

(1) random sampling: take a repo by using the last digits of a public number (like, say, the nasdaq index). Eliminate repo if "too small" or "not migrated", until you have 10

(2) compare 1 year before github to 1 year after. This gives you three numbers: at start of first year(A), at start of migration(B), at end of migration(C). N1=B/A, N2=C/B. If avg(N1) not > avg(N2), you win

(3) serious means 20 contribs in the year

(further terms will be settled upon if you want to bet, before you accept)

---

(btw, I think it might not mean much to VIM that it moved =P)