Ive never jailbroken my iPhone, but if i JB the iPad, what happens to the apps i currently have installed.
it takes literally 2 min. the ipad reboots and all your apps are still exactly where they were. only difference is you have a new app called "cydia" which is a jailbroken app store. just be careful with what you install from there until all the apps are ported for the ipad.