Preview at WWDC likely in June, followed by September launch.
Early Hands-On Impression and Overview of Retina MacBook Pro
Engadget posts a brief hands-on with the new MacBook Pro fresh out of the box, showing how much slimmer the new form factor is than the standard MacBook Pro.
It's 0.71-inches thick, or roughly 25 percent thinner than the current generation Pros (which, by the way, live on -- except for the 17-incher). That's just .03-inches thicker than the 13-inch MacBook Air, but it feels like quite a bit more. Where the Air is tapered, this has a constant thickness throughout. So, again, it doesn't feel like an Air, but it's a big improvement over the Pro.
On the right side you have an SD card reader, full-size HDMI port and the first USB 3.0 port. (Which, by the way, is not blue -- Apple just made all the ports 3.0 and they're all naturally white.) On the other side is the other USB 3.0 port along with dual Thunderbolt ports, a headphone jack and the new MagSafe 2 connector.
The Next Generation MacBook Pro is currently available only as 15-inch model and is available starting at $2199.
Update: The Verge has also posted a gallery of hands-on photos of the new MacBook Pro.