Nav kit plays a part - and the modern moving map GPS is a useful tool to help with that, but it does little to assist with knowing what everybody is doing, what the weather's doing (in the UK anyhow, some models will do that for you in the USA), how the aeroplane is chugging along, how the other people in the aeroplane are behaving, what the next altimeter pressure setting or radio frequency needs to be...
I use a moving map GPS for certain tasks (particularly flight testing where I want to free up a lot of mental capacity for other jobs, another is reliably finding small grass strips I've not been to before, a further is allowing me to manoeuvre around the edge of danger areas with small and thus timesaving margins) and it's very useful in assisting my SA. But as others have said it is just one of multiple inputs into the pilots trained brain (an untrained brain is of little use - doubt this?, try asking a passenger who hasn't flown before, 20 minutes into a flight, where you are and where any other aeroplane is). And it is in danger of encouraging over-reliance on a single data source, which is seldom healthy.
Anyhow, we couldn't have a thread with any navigational content on Private Flying without IO540 banging on about the superiority of GPS, and the utter redundancy of all other navigational methods - we'd all get suspicious and lonely without it.
G