Google might have a winner on its hands with the Chromecast, it's very cheap at just $35, it does exactly what it says it does and it does it pretty well. It's sold out everywhere and those who have it seemed to be hooked to it, streaming all kinds of content all the time. At first it was rumored to be a device running a simplified version of Chrome OS, then it turned out that it has some roots in Android and Google TV, but since it's actually a little bit of both, you can do all sorts of things with it. For example, like any Android device, it can be rooted, so you can mess around the OS but also, like the good Chrome OS device it is, it has stable, beta and dev channels just like the browser or the full OS on Chromebooks.
Developer Jay Lee found a way to change channels on your Chromecast and shared the instructions via Google+, you just need to root it, execute some commands and you're done, you'll be running in beta or dev channels in no time. After a reboot, the Chromecast will apply the update and you'll be enjoying some of the experiments Google likes to try.
You should tread carefully however, beta and dev versions might have some new functionality, but they're usually not ready for the stable channel for a reason: bugs. As every experimental feature in any piece of tech around the world, beta versions have bugs, and those bugs could cause instability or worse, it could even end up bricking your device. Since the Chromecast is a really simple device, meant to do just a couple of things, mostly streaming from different sources, you might not feel the need for beta versions. Sure, you might receive the occasional bugfix or new feature beforehand, but it won't make that much of a difference. I would rather help developers tests their new apps, like Koush's gallery streaming app, than test Chromecast. I've had my fair share of issues with Chrome beta and dev channels, I like the beta channel but I learned to stay away from the dev channel, it's not for everyday users, even power users. I can live with that for a day or two in a browser, but would you want your Chromecast to get messed up?
Either way, people like to beta test stuff, specially Google's stuff. Half of the apps on my phone are in beta and there's a good chance that if I get my hands on a Chromecast, I'll probably end up on the beta channel for a while. I just can't help it, all the risks are part of the fun, but you have to be sure of the risks before jumping in.