> I assume their are values of UTF-8 where it would fail though.  For example,
> if the last byte of a multibyte character looks like a quote or comma.

The last byte of a multibyte character cannot look like an ASCII
character in UTF-8 (it can happen in other encodings however) because
in UTF-8, all bytes of a multibyte character have the first bit set to
1 http://en.wikipedia.org/wiki/UTF-8#Description

Cheers,
Vincent Isambart