I've made some performance improvements to MyFaces here:
I've put together a Pull Request here with the changes:
I know that Thomas had some concerns with using a StringBuilder here and I
think I've addressed those concerns in the description of the JIRA issue.
Doing some profiling of an application with some JSF in it we saw
performance improvements with these changes and as a result I wanted to
Please let me know if you have any questions or concerns.