Various projects that I’ve worked on rely on building efficient hash tables for looking up, well, all sorts of stuff (wow, that was vague). Say, storing transposition table entries in my checkers program. Cuckoo hashing is a way of resolving hash table collisions.

Here are some references:

My Biased Coin: Cuckoo Hashing, Theory and Practice : Part 1
Wikipedia entry on Cuckoo Hashing