For a particular site that only allows GoogleBot to spider, I am seeing Bing has thousands of pages in its index, but the pages have no "blurb" content. (Yahoo has only a handful of pages indexed for this site.)
The pages even appear high in the SERPS for appropriate specific search phrases.
At first glance I thought bing was ignoring robots.txt, but this does not seem to be the case. They must be indexing these pages based on external links.