I think the complaint in this article is laughably petty. I've never noticed a lag. But on the topic of mice, I bought a Kensington mini-mouse about three years ago that I've used with three different laptops (2 Macs and a Thinkpad) and to this day I've never noticed a difference between any of the computers. I would recommend it just for its size and functionality, it's the best mouse I've ever used. I didn't even have to install a driver for it, it just works immediately when I plug it into my Pro. It does feel faster than the trackpad but I think it's just because of the nature of trackpad vs. a mouse and not because of any noticeable lag.
The model I have is very similar to this one: http://www.amazon.com/Kensington-K72346US-Netbooks-Buttons-S...
It used to be on the Apple store website where I bought it but they seem to have removed it.