I've already played half of Resident Evil: Revelations on the Xbox 360, so I don't need a demo. [/sassybrag]
Capcom sent word that the downloadable demo that Japan got is coming to the west soon, to Xbox Live, PSN, Steam, and Nintendo eShop. They say that exact dates will be confirmed shortly.
It sounds like the demo is from the start of the game. You'll play as Jill Valentine, working to infiltrate a cruise ship to resuce lost BSAA members Chris and Jessica.
If you're not one for demos, the full game releases on consoles and PC on May 21, and in Europe on May 24.