On the readability of text/enriched, the one biggest problem I find is the
<nofill> issue. Although these mail composers we've been talking about provide
for automatic wrapping, not everyone uses it. If they actually type the line
breaks themselves, their message comes out with a blank line separating every
line, which is annoying.
On the other hand, if they do that than the text/plain version might also have
ragged <long line>, <short line> pairs (if their lines are longer than the hard
break limit, which is easy to do with a proportional font and a wide window),
so maybe I've been too hard on text/enriched, when generated with as little
markup as possible.
A really smart system might notice whether text/plain or text/enriched would
result in a "prettier" uninterpreted output, and pick that. Ah, that might be
too smart, users also like predictability....