Features:

With the fancy "Intellieye" technology, the mouse proved to be very smooth and accurate, but there are other concerns with mice.  First of all, the mouse should be very comfortable, and it should have useful buttons (wheel for scrolling, and optional buttons.)  The MS Intellimouse Optical is a very comfortable mouse, that's well suited for left or right handed mousers. 

I have previously owned the MS Intellimouse Explorer, and the mouse was just too large and 'bulky,' and was not too comfortable for me.  The MS Intellimouse Optical is my mainstay mouse because it is simply very comfortable for me to use for hours and hours on end.  You get 4 buttons and a scrolling wheel (which can also be used as a 5th button.)  You naturally get the usual left and right mouse buttons with the scroll wheel in between them. 

 However there are also two additional buttons, one on the left side, and the other on the right side.  Using the included Microsoft Intellipoint 3.0 software, you can assign different commands to them.  By default, the left-side button is used for going 'back' on an Internet Explorer webpage, and the right-side button is used for going 'forward' on an Internet Explorer webpage (the buttons function the same way within Windows Explorer.)

Including the PS/2 adapter was really smart, there are quite a few people who have run out of USB ports to use, or they simply just don't have USB at all.  I personally use the PS/2 port whenever I have to dive into Windows Safe mode (as USB doesn't seem to work at all in Safe Mode.)  The PS/2 port adapter is green so that you can not possibly plug it into the wrong port (as long as you have a PC'99 compliant motherboard with the colour coded connectors.) 

Onto the performance of the mouse....