So, with so many travellers (including myself) pissed off at this change - does anyone know an effective place to send our complaints? I, for one, would be glad to register my discontent if I knew it was going to be listened to.

You never know, maybe if enough of us say something Aeroplan will try to do something. I see this as less about United taking something away than Aeroplan not protecting their member's benefits. I also regularly choose United for E+ and am very unhappy about this change, but from YVR most of the US places I fly to are only served by them (or Alaska YIKES!) so I feel caught between a rock and a hard place. I certainly resent being a loyal customer and suddenly being sent to the back of the bus!