There appears to be an issue with HttpWebRequest in this new firmware. I've reduced my code to the simplest test case of making the request and trying to get the response, but it seems to freeze on getting the response (pressing pause in Visual Studio shows that the execution never gets past that line.

public static void Main()
{
    Debug.Print(Microsoft.SPOT.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces()[0].IPAddress);
    HttpWebRequest request = HttpWebRequest.Create("http://example.com") as HttpWebRequest;
    Debug.Print("Request created");
    WebResponse response = request.GetResponse();
}

Any ideas? It also used to freeze on the previous RC's but only if unplugging the network cable, and then re-plugging it back in (or dropping the connection some other way). As a note it works fine in the emulator, so assume its an issue with the firmware.