Software update 4.2.1 (build 2100) can be had by going to your Settings Menu on your Apple TV, then select General and then Update Software. You can also update your Apple TV by connecting it to your Mac or PC with a Micro USB cable and opening iTunes. (Yes, the Apple TV internal version numbering doesn't align with the overall iOS version, which is 4.3 at the moment.)
The update also fixes audio glitches on some TV models, and it adds the patented Apple "stability and performance fixes" we know and love. If you have a second-generation Apple TV get clicking. The update is suggested for all Apple TV second-generation owners.
Important note: Several people are having trouble logging into Netflix after this update. I've confirmed that issue, but I can't bring up Netflix from my iPad or desktop Mac either. Now Netflix has this update on its website. "We're sorry, the Netflix website and the ability to instantly watch movies are both temporarily unavailable."
Thanks to Markus for the heads up.
Apple Apple TV 2nd-gen