The Chrome team is pushing out an update to all the good little Chromecasts of the world. This one doesn't come with any changes to the UI or new features, but it does promise to improve the stability for Google Play Movies playback, and should make Chromecast devices discoverable on more networks. You won't need to do anything to get this installed on your end, the OTA will automatically download and install when it's your turn.
If you happen to be developing an app with the Google Cast Preview SDK, you will want to check out the latest update to v1.0.1. The changelog is even more sparse than that of the Chromecast - mostly bug fixes developers won't notice. However, there will be one very important change for iOS developers: the 'namespace' parameter has been renamed to 'protocolNamespace', removing the keyword conflict for Objective-C / C++ developers. To download the latest version, check out the instructions on from the Google Cast Developer Page.