I've got two of these for Pentax K10d and they are very, very good. Given the other review I recommend that you buy direct from Amazon.
Sometimes I do not use my camera for months or weeks at a time and the battery appears to hold its charge very well. I take a lot of photos when I do use my camera and, despite these batteries being over 2 years old, the times I find myself re-charging them are few and far between.
Only twice have I needed to actually use the spare battery. Even when the camera is telling me their is no charge left they still go on for several shots.
Make sure you get genuine batteries, and you will be pleased.