Tabula Rasa just doesn't make sense to me, I've just finished watching it and don't get how the spell made them all forget. The spell Willow used was only fro Buffy and Tara, so surely the added Lethe's bramble would have just made them forget more than recent things, and not made the whole gang forget instead. Also with the forgetting they seemed to remember vampires but not their own names, Buffy still had the slayer instinct as well, whereas Spike forgot he was a vampire.