I've never felt comfortable giving out my ebay login info to 3rd party services that snipe for you. So, like Howard, I stick with Buy it Now auctions or, if it's something I really want, I'll have a reminder through my phone to alert me when an auction is almost over. If it ends in the middle of night - I'll just bid my absolute maximum as late as possible and hope for the best.
As an occasional seller, I hate the practice of sniping. It discourages "impulse" bidders (instead they "watch" and sometimes forget about it). And it often ends up going for lower than it could have been if any one person isn't bidding their absolute maximum.