so one nil to you .
Good on you for giving it a go.
You are correct it is not the perfect panacea. I have seen people putting in incorrect routes for example. The classic situation is on departure where the pilot has a good mental picture of where he thinks he is going (from looking at the map), sets off, but finds the GPS is telling him to go some where else (due to entering a wrong route). If the surrounding airspace is tight, problems can quickly follow.
Of course the other situation is that of pilt overload. Weather gets in the way, and a few zig and zags later problems ensue.
The first is of course avoidable by a simple logic check of the GPS against what you might expect. Never blindly enter a course in the GPS, just zoom out and check the course looks like the course you would expect.
The second is more difficult to avoid. I think the key is to have a good mental picture of the route and to consider along each leg what your options would be if the weather were to get in the way. This is were it can help to have the route penciled out on your chart as a chart will beat the GPS in terms of enabling you to quickly take in a much larger area of airspace.
Most moving map GPS whilst having some way of showing the lower limits of CAS do not provide this information in an intuitive way. Maps are little better in that whislt the information is printed on the map it is often difficult to pick up the information quickly and clearly. I feel this is one area where both the database suppliers and the map makers to do a lot better.
For this reason I am not sure the chartless cockpit really works unless you are driving something with a G1000. In that case the large screens provide a situational awareness every bit as good as a paper chart. Even then there is a danger, as I nearly discovered recently. For reasons only known to Garmin upper airways are not shown. A recent flight at FL85 would have taken me across an airway, shown clearly on my CAA chart but not on the G1000. I was aware of the airway and the controller was happy to give me a clearance, but had I just been relying on the G1000 I would not have asked for a clearance.