I used to manually snipe. It's quite a rush. However, being human, I'm very forgetful. Some items also end at weird times... and I like to sleep.
I've used Gixen for like ~7-8 auctions so far, and I've won every single one. 4 of those were today: I was bidding on a group of items, and the end times of at least two of the items were extremely close. Probably could never have sniped all of them if not for Gixen.
May just have to get mirror, if nothing else for the API (it's already reliable enough). I made a web app that emails me about new auctions, and a webpage listing the items. Would be golden if I could queue up snipes right from that page.