I've had both the Intellimouse Explorer 1.0 (still have it, still love it, but it's pretty beat up) and the MX1000, which I got for Christmas.
I've heard the Razer is great for gaming, at the expense of ergonomics. This is my biggest problem because I have really long fingers and need a real chunk of a mouse for comfort. The Microsoft was perfect for this (I hear revisions after the 1.0 were smaller though, which is why I hang onto mine); the MX1000 is extremely close. On the other hand, the Logitech is equal or better in precision and speed, and has no cord, and its battery lasts a long, long time on a charge. I love not having the cord, as my machine is a little ways from me, and I hate doing something only to have the cord get caught or all the slack taken up. I'd argue that most gamers who think wireless isn't precise enough wouldn't notice on the MX1000, even if they claimed to notice. Half-Life 2 and Doom 3 play great for me.
The only thing I like about the MS mouse more than the Logitech is the scroll wheel. Logitech's takes a much firmer press for the third-button click than MS, and Microsoft has that nice ridged feel to it. Logitech's isn't quite as nice, but it's definitely usable.