One example I can point to is the fact that we (Sensory Networks) had cargo-culted in a recursive hash function for a string matching engine (back when we made hardware). There was no real reason to be using a recursive hash at all, but there was a cool paper from the NSA about recursive hashing, so there it was. No-one had even evaluated anything simpler.

Again, recursive hashing is cool. Arguably Bloom filters and (maybe) Cuckoo hashes are cool too - but my problem isn't with the existence of these techniques but the way that people seem to get a rush of blood to the head and use them when they're kind of pointless and overcomplex.