Apple has for the first time gone on record to say that jailbreaking your iPhone or iPod Touch is copyright infringement.
Every three years the US copyright office holds a rulemaking session with regards to the Digital Millennium Copyright Act where corporations can file complaints or exemptions.
For the 2009 session the EFF (Electronic Frontier Foundation) filed an exemption request for jailbreaking iPhones for the use of interoperability with independent software (read: anything not in the App Store) to help keep the jailbreaking community alive.
Apple filed a formal complaint that sates jailbreaking is copyright infringement which is not legal. The entire complaint can be found here ( warning, PDF) which states jailbreaking "involves infringing uses of the bootloader and OS, the copyrighted works that are protected by the TPMs being circumvented."
The EFF claims that "courts have long recognized that copying software while reverse engineering is a fair use when done for purposes of fostering interoperability with independently created software."
It could be quite the fight for the two organizations and hopefully it doesn't come down to who has a bigger bank account because it could be argued that the jailbreaking community gave Apple the idea of creating an App store.