I think the GPS is sensational.
Yesterday flew from Goolwa up the western side of the Adelaide Hills, dodging showers, heading NNE, then course change to NW across the hills, dodging more showers, skirting Airspace, then more N up to PT Pirrie, form there it was due N before turning due W across the gulf then SSW to Cowel before turning W to Cleve -- all in the presence of a SW wind varying from 10 to 25 knots. Moving map GPS, spitting out groundspeed continuously with all the changes in heading -- PRICELESS!!!!
I carry 2, use them all the time, have the map out on the passenger seat and cross check -- I have several pre marked tracks marked in 20 mile intervals which I leave drawn on the chart as I use the routes regularly -- I know all the ground marks from previous trips so I don't mark anything on the charts -- I just fly the plane.
GPS primary nav tool, you bet. Runs on planes 12 volt system but with battery backup - unbeatable.