I've been using Blekko for research in a broad range of topics. Yesterday I searched for French grammar rules and was happy with the results (I actually made a purchase because of it).
I quickly referenced Google but the SERPs were far less interesting and diverse.
EDIT: Ah yes, almost forgot Blekko's SEO/competitive intelligence features. Makes for nice client reports.
http://blekko.com/ws/cython+boundscheck http://www.google.com/search?sourceid=chrome&ie=UTF-8...
Blekko results are much spottier. Google results are exactly what I needed earlier today. What domains does blekko excel in?