My dummy load experiment still has a few unanswered questions, but I found that the ARRL Handbook has had a circuit which is basically what I built, minus the one series resistor. It looks like this:
Okay, they use a germanium diode with considerably lower voltage drop, and include a 4.7M ohm resistor in series to the DVM. This circuit also appears on the QRPEDIA posting on RF probes, and apparently is constructed as part of the assembly of the Elecraft K2.
Here's a posting talking about how the different diodes make for different performance.