it a bit of a drag to have to go to settings, and turn off Cell data and turn on Wifi?

Is there and app whereby I can just tap on/off from the screen?

Or am I wrong in my assumption that if you are on cell data when you get to your house the IPAD will not automatically jump to onto the Wifi network.

The iPad will always use Wifi, instead of 3G, if both are available. So if you are outside, using 3G, then come back home, the iPad will automatically connect to the Wifi and use that instead of 3G. As soon are you are in range of a known wifi network (meaning the iPad connected to it at least once) will the iPad connect to that Wifi network and start using that instead of 3G.

That said, there is no other way of disabling 3G service, as to turn it off in the settings. On a jailbroken iPad, SBSettings can be used to quickly en/dis-able 3G, but on the iPad 2 that is not an option, as of now. It is the way it is.