Are you looking for information on accidental interruptions or malicious ones? Your data are probably secure enough if you're using WPA2; anybody trying to hack WPA2 is more than just your casual script kiddie. However, there are plenty of jamming devices out there which could cause severe interference, either by accident or on purpose. Anything sending radio waves around near a WiFi connection, especially anything in the 2.4 GHz or 5 GHz range (depending on what band you're using), can potentially cause a disruption. This includes microwaves, cordless phones, cell phones, cell phone jammers, other wireless routers on a nearby channel, and a myriad of other things.
So in short, if your application requires the user to connect with a secure (WPA or WPA2) connection (I'm not sure if an iPad app can do that or not, but at least you can recommend it), then your data should be secure. As far as disruption, you will never be able to fully control that, since there are far too many environmental factors. I would advise developing your app in such a way that if the network connection drops unexpectedly, or if you start losing packets, it can recover gracefully, either by resending data, informing the user, or whatever else may be appropriate for your situation.