It's the people who bid in the last five minutes that piss me off - I've been trying to get a digital camera for weeks now, and someone always outbids me by a dollar or two, seconds before the end of the auction.
Despite this being summer vacation, I'm not really home all that much, and I'm on the computer for even less time. A lot of the auctions end either during the day (when I'm at work), or in the middle of the night, or when I'm doing other things. I can't plan my life around the ending of an ebay auction. So I have to bid early, even though it's pointless because someone will come in and outbid me by a dollar a minute before the auction closes...
/Sorry about the rant