I gave partial mashing a try via the brew-in-a-bag method recently. I had 1 gallon of water in my smaller kettle for the mash and then 5 gallons in my main kettle at 170.
After letting the grains sit for an hour at ~150 I took the bag and let it drip into the small kettle. Then I took it out and teabagged it a few times in the main kettle. I let it sit in there at 170 for 10 minutes as suggested in DeathBrewer's howto thread. I took the bag out, dumped in the contents of the smaller kettle, stirred everything around for a few minutes and then took a refractometer sample. It read 3.2 brix (1.013 according to http://www.onebeer.net/refractometer.shtml).
Calculating the partial mash efficiency I came up with the following: