We haven't tested the Wireless Explorer long enough to confirm Microsoft's promise of months of use, but it does a couple of cool things to conserve those AAs: When you take your hand away or lift it off a surface, the mouse instantly reverts to a sleep mode (not blinking or powering its optical light source at all, as opposed to the Logitech's slowing from 1,500 to two flashes per second but continuing at that rate even on nights and weekends). The driver software pops up alerts when battery power falls to 34 percent and again at 14 percent.

Besides providing a battery gauge, the driver software provides impressively complete control over the mouse and its five buttons -- the primary left and right buttons, pressing the scroll wheel as a button (which activates an auto-scroll function by default), and the two small ridge buttons above the left thumb rest (Web browser Forward and Back commands by default).

You can choose to assign each button to various functions such as double-clicking; the Esc or Enter keys; editing functions like Select All (Ctrl-A), Copy (Ctrl-C), or Undo (Ctrl-Z); or Windows commands such as Minimize, Maximize, Alt-Tab, or Run. And in a downright terrific touch, you can use different button assignments in different applications -- so the side buttons remain as Forward and Back when you're Web surfing, say, but become Cut and Paste when in Word.

Best of all, however, is the Wireless IntelliMouse Explorer's shape. At the risk of sounding like a commercial instead of a review, it's simply the most comfortable mouse we've ever held -- a sculpted chunk that supports your entire palm, with grooves that cradle your index and middle fingers and a soft side and scoop to hold your thumb. (As with most ergonomic mice, lefties are out of luck, or at least referred to Microsoft's ambidextrously symmetrical $45 IntelliMouse Optical.)

The side-mounted buttons feel slightly high at first, with the smaller Forward button particularly taking a bit of practice. But the Explorer is remarkably cozy just to rest your hand on, and feels almost as good in motion and operation. We hate to be seduced by a mouse, especially a pricey $75 one, yet we strongly suspect this is the ultimate example of the species.

Pros:

• Extraordinarily comfortable shape and smooth motion; cordless convenience
• First-rate, simple yet versatile driver and button-customization software

Cons:

• Drags PS/2 diehards kicking and screaming into the USB era
• $75? That's not a mouse, it's a mink