Shadow charges from shrouding strike in shadowdancer (and I assume, but haven't tested, from shrouding shot and assassinate) don't accumulate unless you have cloak of shadows (2 ED point t3) or shadow form (2 ED point t6). There is a t1 ability and 2 t5 abilities that passively make use of shadow charges that are mostly useless without spending 2 ED points on an ability that I'm not otherwise interested in. Already bug reported it (and probably did on my last character that leveled up shadowdancer way back when).