alt Hacker NewsI haven't been able to fully justify it (and sadly I don't get paid for F# anymore :( ), but there was a competent port of the Scala CTrie structure available [1].
My local benchmarks got pretty decent performance, and often a bit better than the regular built-in concurrent structures, and any excuse to get rid of locks is generally a good excuse in my mind, but it was hard for me to push it when ConcurrentDictionary was fast enough and built in and maintained by a trillion dollar company.