We managed to get out today for a 35 mile ride using my new 12-23. It was a fairly flat route, so we still never went into the granny, but we did use the lowest gear of the middle ring, a 42x23. So far, I am very satisfied with the change. The shifting was much nicer (though I think the new cogs have to get to know the chain a little better). For stronger teams and no mountains, this is really a better setup, in my opinion.
Now I just need a gear indicator. I hate not knowing what cog I am on, and this change has thrown my mental calibration out of whack. The cassette is so far away on a tandem, it is like riding in the dark. I am sure with time I would re-calibrate, but changing bikes so often makes it harder.