A very interesting mailing-list post from Ralph Johnson, one of the authors of Design Patterns. He talks about good and bad Patterns practices.

People who make up-front designs are attracted to patterns, because they think that patterns will help them to have designs with less of the flaws of their current designs. Patterns might help a little, but the real problem is lack of feedback and lack of experience, and patterns do not directly address these problems. If people are both designing and implementing systems, then when they use a pattern, they will quickly learn whether it works and whether it makes their system better. If they are doing paper designs then they will not, and so are likely to use the pattern inappropriately.