I've always been shown to use the RPM as guide to leaning and listening to the engine, i.e. pull the mixture out until you hear a tone change in the engine or a drop on the Tacho then push in slightly??. a CHT gauge is also a good guide too.
Anything wrong with this method guys? serious question for the boffins?
As for GPS i flew the 172S G1000 on the weekend and took both maps had them unfolded to the area and on my lap, PAX asked why i had paper maps I told her "if that goes black (pointing to screen) then at least i'm ready and i know where i am". plus i find the airspace heights easier to read from the sectionals than the garmin....