I have used AS for 2+ years and it is always set to throw in the bid at 2 seconds prior to auction's ending. I have never lost an item unless I just didn't bid high enough.
When I find something I want..I put it on 'My Ebay Watch List', when I decide I really want it, I put my Top Bid in AS and then 'I wait in the bushes'. They never see me until it's all over.
'If you're not worried, you're not paying attention.'