As a bidder, I want the lowest possible price = a GREAT deal. So, I don't want people to even know I'm out there! I don't want them to be able to research my previous purchases to see what I collect, and how high I'm likely to go. Also, if my history shows I know my stuff, my bid can act as a endorsement for others to vote - running the price up.
I use www.esnipe.com to place EVERY bid on eBay, and I have it tweaked so that my bids are made with only 10 seconds left. Rarely am I even on the net when my bids are finally made... Frequently, my bid was the only one, and I got it for the opening price.
Word of Caution: eBay now offers sellers the option of offering "Buy it Now". If your bid is waiting out in snipeland, somebody can use this feature to steal the item before the auction ends.
I've learned a VERY important lesson with eBay; very rarely is something an "I've got to buy this because I'll never see it again". With patience, and time, multiple examples of seemingly unique items turn up! Since my goal is a great price, I'll use esnipe, and wait for a seller who takes a bad picture, or doesn't do the best job of describing an item (so that it doesn't come up in "normal" searches... Esnipe ultimately allows you to use common sense (avoiding the adrenaline rush of the closing seconds decision), and bid the maximum you are willing to spend. Under most scenarios, bidding early can only hurt you...