I actually work directly with companies such as Netflix to resolve such issues discussed in this topic. After working through possible causes, the newest MS Silverlight update has come into focus as the cause. The working solution thus far is as follows. (Remember to perform these steps as Administrator, this can be easily done by right clicking and select "Run As Administrator)
First rollback Silverlight:
To perform a rollback to a previous version generally you can simply uninstall Silverlight from the "Add/Remove" programs in the control panel.
Second Download Silverlight 4:
(whatever version of Silverlight 4, generally the newest version of 4 works)
Third Perform a clean up:
Using your choice of utility software such as Ccleaner or Glary, perform a complete clean up including the reg, and all temps (prefetch as well)
Fourth Restart your machine.
To update Silverlight to the new version 5, simply go to Microsoft for version 5, and download to install it.
Afterwards, you can either test WMC to see if Netflix connects and if it doesn't connect then restart a second time to refresh the settings.
The apparent cause:
What seems to be occurring when the initial update is applied to machines, it tends to corrupt Silverlight completely. These steps provided basically gives your machine a fresh clean platform to install the update of Silverlight.
On some machines, as odd as it may seem after performing the steps and if a second reboot is required, reinstalling the network adapter as well is sometimes required.