I don't mind ASLs if you cam 'make them stick' by which I mean if you can get to the front, and get in a pretty central position in your lane (and not against the railings). I think the problem arises when people make for the ASL and the traffic starts moving when the light turns green - the bikes on the right have to accelerate like s*** off a shovel to get in to the lane, or even to get from the right hand side of two lanes in to the left hand lane, the bikes between two lanes of cars have to go left with a big signal, and the bikes on the left hand side stand a chance of being left hooked.
So, in a general way, BM's advice is good - if you are not darn sure you can get to the front, then wait however many cars back.
My personal beef with ASLs is that they encourage Islington cyclists wearing Converse 'sneakers' and cardigans to go to the front and wobble about on their lamentable steel framed 'fixies' in front of me (hoping to jump the light), so that they slow me down when I take off. I subject these untermenschen to my famous close pass, which involves brushing past them at 40kph and then immediately cutting them up. I award myself extra points for a well-aimed gob.