I think it is a great service and I built a manual version with a server and an old FAX modem. The challenge for me is that with a service, if your infrastructure gets compromised, and you have a fax that I sent to my bank asking them to say 'reroute my checking account', it becomes trivial to have my bank reroute it again. The problem for me with FAX is that it is both massively easy to spoof and considered so freakin' authentic by the folks who demand faxes.