I tell many people of one of my favorite string optimization projects. I was asked to lower the response time of a web service from its current response time of approximately 60 seconds to something much faster. With it being a web service, that meant somewhere in the neighborhood of 1-5 seconds.
I immediately looked to see how the strings were being handled throughout the project. With it using a MySQL back-end, there were many static queries in string objects and string XML node comparisons that were all using the standard string handling techniques.
To make a long story short, after only overhauling the string handling throughout the application, I had brought the response time down to 1-3 seconds.
Find my string optimization guide attached to this blog post. I hope it helps you.