What I think I'm trying to say is that there are two things to keep in mind.
First, the GPS allows you to do things (and in fact, some GPSs implicitly sort-of encourage you to do things) that are not all that bright, or even downright stupid. It starts with the GPS database. You will fly VFR but a lot of "formal" VRPs (as shown on the map) will not be in the GPS database. Made-up waypoints, such as highway intersections, that are great landmarks will not be in the GPS database either. This may tempt you to plan your route using whatever is in the GPS database and nothing else. Which means you plan your route from overhead whatever NAV beacon is convenient, to the overhead of whatever airfield is convenient and so forth. But airfields (and to a lesser extent, NAV beacons) are NOT good waypoints for x-country because a lot of stuff happens in their overhead (OHJs, parachute dropping, aerobatics, glider towing, whatnot), and the addition of x-country traffic is not a good idea. With SkyDemon it's easy to add your own waypoints (just drag the magenta line around) but not all GPSs are like that: Some require some serious fiddling with multiple buttons to get a waypoint in, and some even require you to put in lat/long coordinates. So be aware of this temptation and avoid it. (Similarly, the GPS allows you to skirt the edges of CAS very accurately. In fact, sometimes more accurately than the controllers radar scope is. Even if you are technically in the clear, it might lead to unnecessary discussions. So don't do this.) You are the master of the route, and the GPS is there to help you, not to limit you in your choice of route.
Second, the GPS may pack up at any time. Empty batteries, overheating, malfunction, user error, you name it. It has happened to most of us, and will probably happen again. What is your backup plan in that case? If you planned your route so that it can only be flown using GPS, you've got a problem now. But if you planned your route so that it can also be flown using dead reckoning, visual landmarks, radio navigation or something else, you're going to be fine.
And, of course, there is the issue of being thoroughly familiar with the unit. Particularly with the in-flight actions. Do you know which knob or knob combination gets you back to your "default" ("home") screen without thinking and without fail? (In a GNS430 this happens when you depress the CLR button for a second or so, but that's not obvious.) What are the settings of the GPS with regards to what information is shown? Does it show airspace boundaries above or below track, and if so, what is the vertical distance? Does it show major and minor ground features, how accurate are these, and how can you suppress them? Does the GPS do north-up or track-up, and how can you change between these? How does the GPS represent NAV beacons, airfields and other things, and how can you access information about these? How quickly can you setup a diversion to a new airport if something happens during the flight? Is it even worth starting to reprogram the GPS in case of a diversion, or are you better off asking for radar vectors? Does the GPS even show all potential diversion airfields, or does it suppress some because the runway is not deemed long enough. How long does a runway need to be before being included in the list?
Someone who is familiar with flying with a GPS (preferably your type of GPS in particular) will be able to walk you through all this. Most of which can happen on the ground. But if you spend hours heads-down in the cockpit while flying, trying to figure all this stuff out on your own, you're a disaster waiting to happen.
And that's just for VFR. For IFR flying your GPS may help you in flying departures, airways, arrivals and approaches. Even GPS approaches where the CDI sensitivity changes automatically. This requires more extensive knowledge of the unit, and the logic that it employs to do certain things. If you get a glass cockpit even more stuff will be integrated, giving you even more capability but requiring even more knowledge.