Depending on what firmware you're running the touch might be slower. It could also freeze up from time to time, and sometimes some Cydia apps/tweaks/utilities might mess it up beyond recall (because developers aren't required to update their software with each firmware release and some take their own sweet time getting around to it, which can cause some problems) and you'll have to restore it and rejailbreak it when things go wrong. So really the byproduct of jailbreaking is that you'll spend more time working on your phone, but I for one enjoy it. Once you install and use SBSettings or Backgrounder, you'll never go back no matter how slow your touch gets