Go get it here. This release is significant because they've finally provided a bunch of client-side features through a new generic REST client API called HttpClient. It makes consuming real-world REST services much easier in .NET. I've got several screencasts coming shortly.
Preview 1 focused on providing server-side features for building RESTful services while Preview 2 is focused on providing equally compelling client-side features. The following paragraphs outline these differences (from the CodePlex site):
WCF REST Starter Kit Preview 1
The first set of features in the starter kit is server-side features for building WCF REST services, which enable or simplify various aspects of using the REST capabilities in WCF. These include declarative caching, security, error handling, help page support, conditional PUT, push style streaming, type based dispatch and semi-structured XML support. This functionality is exercised by a set of Visual Studio templates for creating REST services such as an Atom Feed service, a REST-RPC hybrid service, a resource singleton or collection service, and an Atom Publishing Protocol service.
WCF REST Starter Kit Preview 2
Preview 2 of the starter kit introduces a second set of client-side features for accessing WCF and third-party REST services from within .Net applications. The new HttpClient class provides the REST developer with a uniform extensible model for sending HTTP requests and processing HTTP responses, in a variety of formats. The new "Paste Xml as Type" Visual Studio add-in enhances the serialization support in HttpClient by generating serializable types based on XML examples or XSD schema.
Preview 2 only made a few minor changes to the Preview 1 server-side features. The biggest changes were: 1) moving the code from the Service.svc.base.cs file into Microsoft.ServiceModel.Web.SpecializedCollections within the assembly, and 2) moving the REST templates so they now show up as “official” templates (e.g., they're no longer under My Templates). Other than that, the server side features remain the same for now.
I've done a bunch of screencasts on Preview 1 that you can find in the Pluralsight screencast library. New ones on Preview 2 are coming soon.