Rhino 5 Visual Tips is shipping.
Here are the Rhino 5 system requirements.
The current release of Grasshopper only works in Rhino 5.
Most Rhino 4 plug-ins will run in 32-bit Rhino 5.
Most Rhino 4 plug-ins will not run in 64-bit Rhino 5. Check with the developer to see when an upgrade will be available.
There is a new Zoo for Rhino 5.
Rhino 4 and 5 support Windows 8.