Lately we've been using JSON as our text-based interchange format of choice internally. While most of our tools are internal and save this data in a way that's invisible to the user, we still do work with a lot of external tools. For better or worse one of those tools is Excel.  Giac Veltri (Engine Programmer) has put together a JSON exporter for Excel and short presentation that give a bit of background on the plugin. This plugin might not do exactly what you want, but it could be a good place to start if you're also looking to export JSON from Excel.

Included here are Giac's Excel plugins for Excel 2007 (xlam) and Excel 97-2003 (xla) and sample data and the generated JSON.

Have fun!

Updated link to Json plugin! (15 Aug 2010)