I suggest jailbreaking is not a good idea for your iPod Touch 4G with its current iOS version, mainly because it will be a tethered jailbreak. I think you should wait for iOS 5, which should have an untethered jailbreak.
Untethered jailbreaks are easier, mainly because you can reboot and use Safari and Cydia without booting the iPod Touch from the computer. Tethered jailbreaks require a computer around for reboot, using Safari and Cydia, so its a real pain.