Information Today Inc. each year publishes the Enterprise Search Sourcebook. This year's edition was published in print and digitally, with the digital edition actually having more content. On pages 18 & 19(in the digital edition) is an article I authored entitled"An Info Pro's Federated Search Pros and Cons". If you are interested in search (federated or otherwise), then you may want to thumb through the Sourcebook.
This has been out for a while and I am very remiss in not mentioning it sooner.
Technorati tag: Federated Search