Appleinsider claims that the 17" MacBook Pro is slated for release by June 2006, around Apple's Worldwide Developers Conference.
The upcoming MacBooks Pros are expected to ship with "at least a 2.16GHz Intel Core Duo processor". The new MacBook Pro ships with a slimmer form factor requiring a slimmer SuperDrive. At present there only appears to be 4x SuperDrives available at that thickness (9.5mm). Appleinsider speculates that the lack of 9.5mm 8x SuperDrives may be one of the limiting factors from Apple shipping the higher end 17" MacBook Pro.
No word on the expected availability of the 12" MacBook Pro, but the 15" MacBook Pro announced in January has begun shipping to users.