First, thanks for your plugin. I just discover it and honestly it rocks :p
But, i'm french so i Looove weird letters like é,à,è... And the function showexcerpt() don't return the text as a UTF8 encoded text.
I made the modification on my own WP install but it can be cool to add it in the next version.
To do it, just edit the line 48 in excerpt_function.php and remplace it by
return str_replace($morestyle, "".$morestyle."", utf8_encode($content));
Hope it helps,
Greetings from France