Run the YSlow! analyze on the piwik User interface and fix the problems using Yahoo suggestions.
The only point seems to be point 10. At this stage, but such a thing has to be done at build time, or in a post commit hook. We could open a ticket for this if we decide to implement it.
At the current stage, I suggest there is not much we can do that Yslow! advises us.
Thanks Christian for the analysis :)
ticket done. Created #533 to followup our findings