Yep, @Musclenerd just tweeted that iOS 5 beta 1 has already been jailbroken on the iPod Touch 4G:
Screenshots:
http://is.gd/7GxIcK and http://is.gd/BwPvfh

Screenshots:
http://is.gd/7GxIcK and http://is.gd/BwPvfh