I had a problem with your plugin when I installed it - it seems the code you use to detect multibyte string support in mb_find_replace() wasn't working as expected and the code bombed out with a fatal error.
I changed the detection code from:
function_exists('mb_substr')
to:
function_exists('mb_strpos')
which solved the problem.
I'm not familiar with multibyte string functions so I'm not sure why my fix worked but it did :)
Jonny