Interesting approach. Doesn't keeping and hiding the original FVWP result
in a lot of overhead?

My main problem  with custom  forms tends to be the whole Parameter/Filter
issue, whereby I say "create a parameter called ID and fill it with ID from
the Querystring"... usually when I do that through the GUI, I get an ugly
error in Design mode and end up just hand-coding the param (and sometimes
the filter CAML as well).

Seems like there's too much "fuzzy" involved in this process; I can't wait
to spend some quality time with SPD 2010 so I can plan the appropriate level
of disappointment for the next few years.