First and most importantly, on November 7th we uploaded WCF Data Services 5.1 to NuGet. "5.1" is a deceptive version number - this release of WCF Data Services is arguably one of the most important releases as it contains the new JSON (formerly JSON Light) format. We expect this format will become the preferred format for most OData services in the future.
This release also has built-in support for $format and $callback, and some new client-side events for interacting with requests and responses. This release has been eagerly anticipated both inside and outside of Microsoft, with over a thousand downloads of the release candidate packages on NuGet alone.