For an iPod touch? It's probably legal.
Nobody knows for sure at this time, though. Even less so with the iPhone.
Some people say yes, some people say no. Apple says no, at least for the iPhone. As of right this minute, there is nothing stopping you nor will you raise any eyebrows if you do, indeed, jailbreak your iPod touch. The legality of it hasn't been determined yet. Meaning it's pretty much ok to do until a definitive legal status is established. Does that mean "legal?" I dunno. Maybe.
Perhaps there's a specific difference between the iPod touch and the iPhone that would allow for jailbreakage of one, but not the other -- due to the way the FCC handles wireless/cellular networks vs. how they handle wired networks.