Good, technical article about DisplayPort vs. HDMI:
http://www.edn.com/index.asp?layout=article&articleid=CA6594089

Most interesting factoid: DisplayPort is certainly the "right" way to go and, if not for HDMI's widespread adoption, would have otherwise completely displaced it. Despite this, DisplayPort is also aimed at supplanting LVDS, the way that digital signals get from your laptop to its screen. That, alone, could drive all of the necessary chipset volume to make DisplayPort a success, even if it fails to get traction in the consumer space.

It appears you can get several Dell monitors with DisplayPort (and VGA and DVI and lots of other crud). It's not at all clear that you can get a cable to go from the MacBook's Mini DisplayPort to the "full" DisplayPort connector. Unless Apple offers one at some point, you're out of luck.

For backward compatibility, if you believe Wikipedia: "The video signal is not compatible with DVI or HDMI, but a DisplayPort connector can pass these signals through."