Just a few words on the IM Explorer (even if they are a few days late):
1) Mouse Rocks! Don't ever have to deal with jumpy cursor again... no cleaning of mouse balls, etc! I originally thought the size was too large, but, it is actually quite comfortable once you start using it. I prefer it now over the old "tiny" intellimouse size.
2) There are issues with this mouse. I had a problem with the left button doubleclicking in place of single clicks. It does it randomly. I called the 1800 # (which I don't have handy right now) and they asked for the serial and sent me a new one. They were backordered so it took a while but when they shipped it came 2-3day mail.
FWIW, I think the problem was not in the button mech but in the cable. As mentioned earlier in this thread, the cable is very sensitive to tension and over time will degrade (Apparently). I've had the new mouse for almost the same amount of time and this one still works fine, so, it may be a design flaw that they've later fixed.
3) There are bugs with Video Drivers, Intellipoint Software, and Scrolling in IE 5.x. When using the mouse wheel, various issues (such as machine hanges, etc)... only if you are using the intellipoint software that came with the mouse. (Problems go away with default drivers -- uninstall intellipoint software).
My specific problem is if I scroll up to the top of a web page and keep scrolling the wheel up, it goes back a page. VERY ANNOYING if you were trying to get back to the top and scrolled once too many. (I looked for a setting to disable this thinking it was a "feature" but have not found it yet, so I am using the default drivers and have uninstalled the intellipoint software--latest version was 3.2
So, other than the problem with the intellipoint 3.2 software, I've had 0 problems with this replacement mouse. The only online FPS I've used this with is Unreal Tournament and the mouse is not holding me back at all... I wish I could say it was!

In fact, it has definitely improved my tracking and accuracy.