Anyone who does claim that fax works well over VoIP is full of shit - in my opinion. If you're an occasional faxer, and only send short faxes you'll likely have pretty good luck with VoIP - but in most cases, you'll have better luck with a dirty but functional PSTN line (V.34 modems are pretty tolerant of noise) I'll note though, in many cases, the desire by the carriers isn't to replace copper - its just to eliminate PSTN service - see AT&T U-Verse, which is FTTN, not FTTP.

Either because of poor implementation or a lack of universal uptake T.38 doesn't seem to solve the problem well enough to resolve the issues.

E-Fax is the current best end solution - but adoption is slow, or lacking.

What I'd like to see is a universal, easy to use encryption system come into use, so we could just send this stuff over email.