How To Add Log4net and Logging into your Umbraco 7 Website
Jon explains how to set-up your own custom log files.
Log4net logging from your custom code in Umbraco
Article by Darren Ferguson explaining how to log using Umbraco. Seems a little wrong.
logging - load-balancing - Server-Setup - Setup - Getting-Started - Documentation - our...
Load balancing considerations for older Umbraco versions ( <7.5?)
Azure cloud logging option using Azure data tables. Interesting but proceed with caution.