If you are already familiar with it and want to try it out right now go to Blekko and do the following search
You will need to enter /aarontay/library to indicate that you are using a slashtag created by me.
Other slashtags you can use created by me include
aarontay/library - covers all of the above slashtags
site counts are as of Nov 13.
What follows will describe how I created the slashtags and a little review of Blekko from librarian point of view.
In fact you could download by region for academic libraries & public libraries in USA, and by countries for the non-US libraries, so you could create very granular slashtags such as /northwesternacadmic libraries and then combine them into bigger and higher order slashtags (see later) but I wasn't interested at that level of granularity.