I think the most amusing case of UTF-16 considered harmful would possibly be the choice, in WPF/Xaml, to use UTF-16 code point offsets to reference positions in XML strings -- while supporting UTF-8 XML encoding. It can create the situation where, even if the input and output are both UTF-8, you'll nonetheless need to transcode into then out of UTF-16 in order to perform the proper string splitting.

Fun.