I've been wondering a bit about this too. The iPhone's been hacked basically, you're now able to install a few third party apps and change around icons and backgrounds on your iPhone. From the looks of it, the iPod Touch runs the same OS as the iPhone, and thus I'm sure someone will hack into it soon enough. I don't know if I'd do that though.
May I also remind you however that the iPod Touch will be compatible with all of the iPhone apps that developers have made for Safari. And there is quite a lot of those.