The beta works with all Intel Macs and allows you to virtualize a number of different operating systems. You can assign multiple processors to your virtual machines, and Fusion supports USB 2.0 out of the box. One of the largest selling points of Fusion, besides VMware's track record, is that you can download and run a number of Virtual Appliances which run the gamut from a complete Oracle 10g environment to a lightweight Knoppix install. As with any betas, there are bugs so make sure to read this page detailing them all.
Read on for some pictures of the beta in action.
The window that greets you when you first run Fusion:
Setting up a new Virtual Machine:
The list of operating systems that are supported:
Various flavors of Windows supported:
A virtual appliance starting up: