A common complaint about patterns books is that they have nothing new to tell experienced developers. (I've had a few of these recently in amazon reviews and on The Server Side, so perhaps I'm feeling sensitive at the moment.) Not just is this true, but it's the whole point of patterns.

Patterns are there to capture knowledge from the field, not to present original ideas. As a result it's inevitable that patterns books aren't going to add stunning new ideas to those who have been working in a field for a while. But even so I think there's an important role for patterns books even to those who don't need to learn the ideas. This role is to help the experienced people communicate their experience to those around them who are less experienced. Few teams consist of entirely of seasoned developers. One of the most important things an experienced leader can do is pass on her skills.

(For more on the role of patterns see my IEEE Software column.)