No, the GC would pick up the unused queues/queue elements (the Immutable Collections aren't necessarily immutable inside the data structure itself ;)). Check out the Channel9 vid about them, it's pretty cool: http://channel9.msdn.com/Shows/Going+Deep/Immo-Landwerth-and-Andrew-Arnott-Inside-Immutable-Collections

Anyway, we aren't using them right now so it doesn't really matter :).