This is a very nice, useful and elegant plugin.
Yet let me propose:
1. So that the number of footnote within the text is more distinguished and legible I propose to have it like e.g. (1) or /1/.
2. As the native language of my websites is not English I have to translate the word 'Notes:' into my language (i.e. Czech). I did so by editing the simple-footnotes.php, which is impractical as to the plugin upgrading.