Jailbreaking is NOT illegal. Don't listen to anyone that says that. Apple has taken this to court many times in different countries and lost everytime. Once you purchase their product, it's to your discretion what you want to do with it. However, it will void your warranty, and using the jailbreak to download music, apps and video illegally, is obviously, illegal. Just search "best ios 6 cydia tweaks" and you'll want to jailbreak.
don't listen to everyone else. a cop probablly wouldn't arrest you if he saw you on the jailbreaking app. but there IS a downside, however. the upside is that you get an awesome app that lets you have awesome free stuff,.... and the bad side is, in the proocess of installing it, your ipod could malifunction, and you have voided the warrenty.