One of the main resources to visit when developing applications for SharePoint was updated this month (Feb 2009). Go update your favorites and read away.
To ensure that your SharePoint system performs at its best, you need to be able to answer the following questions about the code you write:
Does my code properly dispose of SharePoint objects?
Does my code cache objects properly?
Does my code cache the correct types of objects?
Does my code use thread synchronization when necessary?
Does my code work as efficiently for 1,000 users as it does for 10 users?
If you consider these issues when you write your code, your SharePoint system will run more efficiently and your users will have a much better experience. You can also help to prevent unexpected failures and errors in your system.