I just saw this over on DPreview -- not exactly HVX-related, but occasionally someone will ask how to get higher framerates than what is possible with the HVX. This might be a possible alternative if you need 10x or more slow-motion:
http://www.dpreview.com/news/0708/07083101casio300fps.asp
http://www.dpreview.com/news/0708/07083101casio300fps.asp
