i know some people are worried about jailbreaking their iphones and i think its mostly the name that does it.
but look at it this way. apple is continuously making new firmware updates each one locking out jailbreaking and locking your phone to a specified provider. if you dont like the new firmware version then bad luck you have to put up with it for good.
what the guys from cydia have done is they now log your shsh files for what ever versions of firmware you are using with a jailbroken phone which allows you to go back to older versions whenever you like. it allows you to personalise your phone with ring tones themes and all manner of things that apple could let you do but chooses not to.
you get access to heaps of free (not illegal just free) apps which you cant get on itunes (apple charges money for the right to submit an app and reserves the right to say no after they have taken your money this alone puts many people off submitting a app that will be free or accepted by a limited audience)
jailbreaking your phone is not illegal. courts have ruled that you are not breaking the law by jailbreaking.
apple is now persuing other ways to turn people off jailbreaking and hopefully they lose in this attempt.
i use jailbreaks to unlock the phone and to personalise it. i still use mostly all itunes legitimate apps and some others from cydia which arent available on itunes.
jailbreaking has not in anyway affected the performance of my phones.
please take the time to support such organisations as modmyi and cydia and the many many others who allow these freedoms with your iphone ipod touch and ipad products