The germ for this question came up from a discussion I was having with couple of fellow developers from the industry. Turns out that in a lot of places project managers are wary about complex data structures, and generally insist on whatever exists out-of-the-box from standard library/packages. The general idea seems to be like use a combination of whats already available unless performance is seriously impeded. This helps keeping the code base simple, which to the non-diplomatic would mean we have high attrition, and newer ones we hire may not be that good. So no bloom filter or skip-lists or splay trees for you CS junkies. So here's the question (again): Whats the most complicated data structure you did or used in office? Helps get a sense of how good/sophisticated real world software are. 
What is the most complicated data structure you have used in a practical situation?
data structures
Have used skip lists for lookup. Where I work, there is a standard implementation and everyone is encouraged to use it. Have used patricia tries for storing and retrieving ip addresses efficiently. Again implementation was already present.