I mostly agree with Rory. There are "licks" that you can play on the keyboard in certain keys that you can't play in others. I emulate guitar a lot and occasionally find it helpful to transpose, even though I can play in most all the keys.
For example, try playing Last Date in C#. Sure you can do it, but it wouldn't sound like it's supposed to. Of course I can't think of a reason to play it in C# anyway.
I think it would be difficult to cover a lot of songs in certain keys. How about Green Onions?
However, most of my transposer use is when I'm backing a "vocalist" who wants to sing in a key that is uncomfortable for me.
I do understand why some people don't have a problem with it. I have a vastly-talented blind friend, who has perfect pitch, and it drives him crazy to play a note and have it sound like a different note. He can tell when a note is sharp or flat by only a few cents. I imagine Rory has that ability as well.
Excellent post, Rory, and a good thread.
DonM

[This message has been edited by DonM (edited 06-02-2010).]