My friends and I were discussing this recently. In my opinion GCSEs have two objectives: firstly, to provide qualifications for employers to assess the candidate's academic ability, and secondly, to provide the skills/ knowledge to pursue those subjects to a higher level (A-levels, IB etc.).
Personally I think GCSEs fail on both counts. In regards to the first objective, GCSEs are quite easy. Most exams require only the smallest of efforts to get a pass, and little more to get a 'decent' pass; with only the tiniest of aptitudes being required for an A/A*. Employers are going to be none the wiser as to the academic ability of the candidate when the tests on those applicant are found to be wanting.
In regards to the second point an example would be useful. My first lesson of AS chemistry and the first thing my teacher says is: 'forget all you have learnt in chemistry before - it was too easy and simplistic.'The jump from GCSE to AS is ludicrous, of course as you climb the educational ladder it should get more taxing - but my chemistry class had straight A*s/ As in chemistry GCSE and only a few of us got As/ Bs - with most getting Cs and some Ds. I think it is therefore fairly safe to say that GCSEs are pretty useless for preparing students for further education.
Additionally why on Earth do they teach us such simplistic theories, if they are only to be shown to be wrong next term...
As a slight counter to my 'rant' - GCSEs are useful to some extent for some candidates who struggle academically. A friend of mine is going to join the army; he had no interest in academia and struggled academically. If GCSEs had been any tougher I think he would really have been in trouble. So I will say that GCSEs do provide some 'entry level' qualifications and are useful for those who struggle academically and have no wish to pursue those subjects or will ever use them.
Anyways, these are just my opinions. What do you guys think?