Absolutely not the be all and end all. One might even say a waste of time.
Out of CTC, Oxford and GAPAN aptitude tests, one told me that I had "absolutely no chance", one told me I scored a "good average", another said I had "excellent chances of sucess in flight training". Which maybe says a lot about the relative validity of aptitude testing.
In the end, I passed everything first time, was fortunate enough to get a 737 job after training and have had good results in the 6 monthly sim checks and annual flight checks with the company.
Don't want to sound bitter but I do beleive that the aptitude testing system failed to give me a conclusive or accurate answer.