Got this great tip for making it much easier to use IIS logs for troubleshooting client problems. IIS logs are notoriously hard to read, and can generate a large amount of data very quickly.
A developer on another team gave me a great tip. First make sure that your capturing the query string in the IIS logs. Then when users run into an issue have them go to the very end of the URL and type in 'ihadanerror' and hit enter. This will get logged and make it easy to find when they had a problem.
Such a simple tip, and it's made such a huge difference in the usability of IIS logs.