Why you need to be developing all your custom code within the feature framework and deploying these as WSP (WSS Solution Package) files.
To develop web parts that are easy to use, easy to upgrade, and secure, you'll want to keep these best practices in mind.
All resources need to be managed—which means you need to make informed decisions about how to store and retrieve resources even for custom web parts.
SharePoint's Web Part lifecycle and handling sequence is critical when dealing with custom Web Parts that have multiple connections.
