This isn't the article that I set out to write. While researching another article (coming soon) I soon realized there just isn't a lot of good material on how to troubleshoot Web part deployment, or even precisely how Web part deployment via STSADM even works. This article is designed to explain the moving parts of the deployment process and describe what can go wrong. Hopefully, it will help a few people get their implementations up and running more smoothly.
http://www.devx.com/webdev/Article/29352