Hans, I did, but I'll try again:

sudo texhash

And got this response:

Password:
texhash: Updating /usr/local/teTeX/share/texmf/ls-R...
texhash: Updating /usr/local/teTeX/share/texmf.gwtex/ls-R...
texhash: Updating /usr/local/teTeX/share/texmf.local/ls-R...
texhash: Updating /usr/local/teTeX/share/texmf.tetex/ls-R...
texhash: Updating /var/tmp/texfonts/ls-R...
texhash: Done.

Mktexlsr seems to do the same thing:

011-101:~/tmp davidarnold$ sudo mktexlsr
mktexlsr: Updating /usr/local/teTeX/share/texmf/ls-R...
mktexlsr: Updating /usr/local/teTeX/share/texmf.gwtex/ls-R...
mktexlsr: Updating /usr/local/teTeX/share/texmf.local/ls-R...
mktexlsr: Updating /usr/local/teTeX/share/texmf.tetex/ls-R...
mktexlsr: Updating /var/tmp/texfonts/ls-R...
mktexlsr: Done.

Then:

011-101:~/tmp davidarnold$ cat junk.tex

\definetypeface[david][rm][sans][iwona][default][encoding=texnansi]
%\definetypeface[david][mm][math][iwona][default]

\setupbodyfont[david,ss,10pt]

\starttext
This should work.
\stoptext

And, no luck. Log file attached.