And if I'd looked just a wee bit further than the pod, I'd have found ~/Spreadsheet/WriteExcel/examples/csv2xls.pl which does this exact same thing.
Yes, but yours is nicer. ;-) In fact if you don't mind I'll include it in the Spreadsheet::WriteExcel distro. Since your version deals with generic separators you could re-target it and call it text2xls.
Just a few notes:
Parsing CSV is never as easy as it seems, therefore, for more general applications it is worth considering Text::CSV_XS or Text::CSV. If the stated purpose is to split on a single character then your method is fine.
# Prettify row as header.
Prettifying the first row is a good idea. Unfortunately, it won't work like this because set_row() defines the default format for cells written by Excel and not for cells written by WriteExcel. This is easy to fix.
# Unfortunately no support for "freeze pane"
Freeze panes will be in the next version. It is a feature that a *lot* of people have requested.
For anything more than a single line of usage the POD::Usage module is worth considering. This keeps your POD and your usage synchronised. It is also one of the core modules. I tend to use it in any program where I use Getopt::Long. It is a useful module and a clever idea.
Todo: binmode(FH) on xls outfile for cross-platform support.
This isn't required. Spreadsheet::WriteExcel will take care of binmode() for you. It only applies if you are creating a new file based on a filehandle as opposed to a filename.
A useful feature would be an option to split the input file into pages based on ^L, or some other delimiter, and put each page on a new worksheet. This is something that I wanted to add it to the csv2xls.pl example but I didn't have time.