I carry GPS most of the time, and have it switched on. However, I never rely on it as the sole means of navigation. In VFR/VMC, I make sure that 100% of the time I know where I am by eye. When IMC or out of sight of the surface, I make quite certain my route and waypoints can be navigated entirely by radio nav.
Frankly, GPS is more accurate and more reliable than the VOR equipment in the planes I fly (and much more so than NDB/ADF navigation). But even GPS fails. The most common failure (for me) is inaccurate programming of the route or the waypoints, or other finger trouble. And I update the database only every couple of years, so airspace boundaries are not be relied on.
My policy, except on local flights, is always to have two independent methods of navigation. But that's just me. I'm not going to argue with anyone that says they always/never use GPS/DR/radio/INS/divine-guidance or whatever.