Whelton announced yesterday that he has managed to bypass the device's cache comparison and install a Springboard hack. "The springboard hack," he writes, "is just the removal of a app and creation of a blank space. Not that amazing, but what's important is the bypass of Nano's cache comparison, which compares any modded SB file and reverts it if it doesn't like it, this opens up the possibility of hacking and modding, while not adding bootloaders or any of that fun stuff."
It's worth pointing out that this isn't a jailbreak. You can't add new apps to the nano - at least not yet.
The hack is just the first step in allowing other developers to play around with the nano OS. For his part, Whelton has made several interesting discoveries about this: "the device's plists of reference to support of Movies, TV Shows, Apps, Games, vCards, Calendar events and so on, with a few other cool things like a passcode lock."
Whelton says he'll be posting more information on the hack on his blog NanoHack.me. In the meantime, what apps would you like to see on the new nano?