*bump*
I've run an upper grille block for a while, just recently started experimenting with a lower block as it got colder outside.
The lower one is hard to see because of the light, but it's a section of *cough* kitty litter box that I trimmed to fit. There are a couple of bolt heads or something toward the back of the top that allow me to "snap" it in place. There is a little duct tape at the top anyway, and I cut out the corner for the block heater cord.
The car is just old enough not to support a ScanGauge/UltraGauge, so I'm admittedly running blind on engine temps. I keep an eye on the stock temp gauge, and haven't seen anything unusual in the trips I've taken so far. I'll no doubt remove some of the tape and open up one of the blocks once spring rolls around.
My commute to work is only 5 miles, but the temp gauge gets up to the midway point and the heater can blow warm air by the time I get to work on days below 15°F, so I *think* it's helping.
P.S. Just for the sake of my engine/FE, though, I don't actually use the heater unless I have passengers.