Public sector & enterprise won't switch wholesale, but they are going to switch the vast majority. The UK Parliamentary ICT Service is planning the switch after the 2015 elections, saying only a small amount of House data needed a high level of security, going on to say, the assumption for maximum cloud storage was 80 per cent of all data.
In a blog post Microsoft lays claim to Kansas City, MO; the City of Seattle; King County, WA; the San Diego County Regional Airport Authority, Dupage County, the University of Miami, the University of Colorado Colorado Springs, Sacramento (Sacramento State) and California State University, all using 365.
Like i said the more users in an organisation the cheaper it is to use 365, it's one of the biggest selling points for 365, with the handy info-graphic in the above linked blog post showing the city of Chicago saving $1.3 million over the next 4 years, and an %80 decrease in the cost per user. The way Microsoft is pricing 365 at this moment in time reduces TCO substantially, whether that will remain true in the future is not known.