Cast vs. As
http://www.codeproject.com/KB/cs/csharpcasts.aspx
Performance Thoughts/examples
http://www.codeproject.com/KB/cs/effective1.aspx
http://www.techgalaxy.net/Docs/Dev/5ways.htm
StringBuilder
http://support.microsoft.com/kb/306822
http://www.codeproject.com/KB/cs/stringperf.aspx