Chris Fry just got $10M in stock options as Twitter prepares for public stock offering. He previously drove an all-at-once transformation of SalesForce.com to Scrum which helped make it the company with the highest return on investment year-to-year for most of the last decade (see Steve Denning's article for Forbes). Guess he is probably worth the money.
I was involved in a similar transformation at Pegasystems a few years ago. 27 teams in two months vs. 30 teams in 3 months at SalesForce.com. Pegasystems stock price quadrupled during the transformation so all-at-once Scrum can be worth a bundle of cash. We wrote about the Pegasystems effort in this paper:
J. Sutherland and R. Frohman, "Hitting the Wall: What to Do When High Performing Scrum Teams Overwhelm Operations and Infrastructure," in Hawaii International Conference on Software Systems, Kauai, Hawaii, 2011.
There is a lot of talk about scaling Scrum recently. Before you adopt any approach, ask them to "show you the money!"