Tron,
I like it because it shows all fourteen channels at a glance, and it shows interference levels. The software that came with my Orinoco and Linksys cards only shows signal level on a specific channel, and only if you are associated with an AP.

Marlon has an explanation on the site of how he's used it in a couple of locations and tracking problems. It depends on what info you are looking for. Slightly different tool for a different view of the 2.4 spectrum.

Cheers,
Thorn