A good read, containing little or nothing of relevance to GA.
The Volpe GPS Vulnerability report (online somewhere I am sure) is more practical, showing that a proper roof-mounted GPS aerial is pretty important to signal integrity. Everybody using a GPS should read it, IMHO.
Ultimately, one still needs to use paper charts for ground based flight planning, have a printed/handwritten plog so one can see where one is supposed to be going, and use TWO navigation methods, of which GPS being one is great.
Flying in IMC solely by VOR tracking and getting a VOR failure is no worse than flying in IMC solely by GPS tracking and getting a GPS failure. But you get a lot more bollocking for the latter.
And at the VFR level there will always be somebody who goes up without any planning and whose GPS batteries go flat, and he will be made an example of for years to come. But if he didn't carry a GPS, he would be just another fool. Not really relevant to GPS!