Too the best of my knowledge Inktomi was the first search engine to perfect directory building from spidering. Huh? They run a spider and then build an ODP/Yahoo style directory out of the data. They can do it on the net wide, or build specific niche directories at a customers request. It is very intelligent software and was some of the basis for my Themes article because it *is* a theme'ing spider/engine.
The /cat spider is the Catalog or directory spider. It is a good thing to see on your site. You have been choosen for one reason or another to the /cat treatment. This could mean big hits down the road. The only problem at this point? very few companies are using the Inktomi generate directories. They are very small at this point - I don't know of a single public one not behind a serious firewall (they have built a few for corporate intranets) and the technology is a year old this month.