I have had 3 snipes not go through, they were *not in time* or *did not win*, which I was told was due to no response from ebay.
That said, I still find AS reliable (I use 8 seconds) and not being from the States - dont have the *heavy* traffic problem, so never adjust my lead times.
I am SURE you will get an abundance of snipers come in a give you all *their* success stories and how many snipes etc, but that doesnt change the fact that you have been bitten.
What I did when I had my doubts about AS reliability was to weigh up my other options.
I'll admit I went to the competition (and still use them as back up), the only other thing I could do was sit at my PC and snipe manually.
My strategy now - low priority auctions that are a dime a dozen, I use AS to snipe as I know another will be along shortly if something happens (havent had that *something* scenario alot).
Medium priority auctions, snipe and manual bid.
MUST HAVE auctions, 1 snipe set at 15 seconds and another at 8 seconds...sit at my PC nervously waiting to place a Manual snipe.
The last option is my least favorite obivously.