I don't think it's a waste. The only reason I bought an Xbox was so I could get MO, and thanks to that decision, I have many other games that I couldn't get on other systems. I agree that playing AO "on the go" wouldn't be the best idea, as you can't have the car, bus, or train moving about as you're trying to concentrat on a level, but playing the game could kill a
whole lot of time when you're waiting for something, or have nothing else to do.
I myself wouldn't get a PSP, as I would like to purchase a DS first, but playing AO on the PSP would indeed have its benefits. Plus, whomever enjoys Playstation games could just go out and get them for PSP in addition to downloading AO onto it

.