So far, the answer to the original question appears to be two letters long.
I'm of the considered opinion that only a small minority of posters on this forum actually tour. We too are trying to decide whether to get an iPad to take on tour. The key advantages are size/weight. I don't think of it as a potential substitute for a Garmin ETrex Vista (as far as I can tell there is no mapping where there is no signal, and it only runs 10 hours on a charge when in use). But as a potential substitute for a netbook or laptop, perhaps.
I too will be interested in any responses from folks who have actually used one on tour.