Here is a long discussion about SVG-rendering, which tends to be slow in leaflet, compared to other libraries: https://groups.google.com/forum/#!topic/leaflet-js/_WJquNpdmH0

Norbert Renner did some improvements, some of which change leaflet's functionality, but is there anything endusers can do to improve performance?

non-optimized: https://gist.github.com/nrenner/7535077
optimized: https://gist.github.com/nrenner/5635334