Isn't it the most accurate and reliable bit of equipment that even a simple UK PPL can use for navigation - in fact if IO540's and other's comments are to be believed it is always the best thing available.
If we assume a simple UK PPL has no IR, then the answer is NO. The most accurate and reliable bit of equipment is your eyes, and GPS will only ever be a supplementary aid.
GPS may be managed by the USAF, but this does not mean it was designed strictly for aviation use - far from it. Aviation users are a minority group. The use of GPS in the aviation IFR environment is problematic, and has many facets. One of the crucial factors is integrity monitoring, and the integral GPS monitoring system does not meet aviation requirements - no secret, and a long known limitation. Equally, GPS is prone to jamming due to the extraordinarily low signal strengths involved. No secret, and a long known limitation
GPS IFR receivers & systems use a number of autonomous methods and/or augmentation to overcome these limitations, and operational requirements are put in place as a safeguard. The USAF ops requirements do not seem to be that dissimilar to civil legislation in many countries that have been using GPS IFR approaches for many years. In my own experience, those safeguards have rarely been required - but the operating environment is considerablely different to radar soaked Euroland.
GPS is not some sort of all encompassing navigation panacea - especially for the aviation segment. But it DOES work 99% of the time - you just have to understand how it works, why it sometimes doesn't work, and have a plan for the latter. But that applies to a lot of things other than GPS