Hi,
I tend to use 8 seconds as my lead time, but I am in Australia and we dont seem to have the *heavy traffic* problems that .com encounters.
.com users tend to use a few more seconds if the auction ends on the quarter, half or exact hour (this is to compensate for all the auctions ending at the same time).
Be mindful that AS *may* adjust your lead time if it detects a lag in ebay's response time and one of the best tips is to use an odd amount when sniping....like $20.58 instead of $20.
Oh - and the ever important...its not the last placed bid that wins, its the highest.
Happy Sniping
PS...Ricks link probably say all that and more