In the area between the split keys resides a two-way toggle that lets you zoom in and out of the active page. Below the spacebar (and between the wrist pads) are two buttons--back and forth--that allow you to move between Web pages without having to reach for your mouse. Both features are welcome additions, as they cut down on mousing.
The Microsoft Natural Ergonomic Keyboard 4000 offers a couple of additional features that will appeal to those concerned about repetitive stress and proper wrist alignment. The two halves slant down from the middle, allowing you to keep your wrists in a more naturally rotated position. Also, the keyboard comes with a snap-on riser that gives the unit a bit of a backward slant, which prevents you from flexing your wrists. Some sort of faux leather covers the built-in wrist rests, giving them a smooth yet supple feel. Although the wrist rests are padded, they're still rather hard and not nearly as comfortable as the gel wrist rests you can get elsewhere.
Microsoft offers a three-year warranty on the keyboard and free phone support for the first 90-days--after that, support will cost $35 per request. Microsoft's support Web site has a searchable knowledge base, FAQs, and software updates. You can also access chat and e-mail support at the company's site.