I've just recently started to level my lock and have glyphed for Dark Apotheosis, but I'm a little confused about one of the abilities it grants. It turns Shadow Bolt into Demonic Slash, which grants 60 fury per hit, but then it seems to dump all but 200 of your Fury when you switch out of DA. It seems a bit pointless for the form to grant you an ability that generates fury if it's just going to get rid of it as soon as you switch out of the form.
I don't really know all that much about locks at later levels though, is there another use for Fury later on, aside from it being a resource for use in Meta form?