Bidnapper actually works. Their support is great and the program functionality is excellent. Do not even think of using PowerSnipe unless you want heart ache and no back up. All they are interested in is getting your money and then ignoring you!
The only additional functionality that would be nice is a research tool enabling search and reporting of items you are interested in bidding on, similar to Powersnipe. Only a minor suggestion on my behalf sai am completely happy with Bidnapper.
Support is excellent. When eBay were altering and reviewing their security settings, Bidnapper were right on top of it and their customer support team resolved the issue quickly while providing advice to me. Of course if your highest bid is lower than others wanting the same item, then it doesn't matter what bidding program you use, you won't win the item.