Things that worked well? Great upper management support though some pretty stressful times. Couldn't have done it without them.

SUers did a marvelous job of pulling together, making difficult decisions that crossed department lines and doing a tremendous amount of work in a short period of time.

Downtime is something no one likes to think about, but it is most likely to happen when you first go up. For that reason, you really do not want to pass go-live without some plan for if it (when?) it happens.