Demiurge said:
It is the best measure of cognitive ability that has been devised to date.
This is true. However, that does in no way mean it is good enough for anyone to be able to say what IQ they "have". An IQ test measures the ability to take a specific IQ test. The tests are really poorly standardized and often incorporate questions that are completely irrelevant when it comes to intelligence. If we are able to agree that intelligence is decided by genetic, rather than environmental factors, it would be interesting to see anyone explain why the average IQ has increased sufficiently in western countries the last 50 years. Such an increase is not congruent with Darwin's theory. The only proper conclusion would be that the tests measure the wrong aspects of the human mind.
One thing that also annoys me is the amount of people who are convinced they are some sort of geniouses after taking an online IQ-test. Take the site iqtest.com as an example. The main site says "Our original IQ test is the most scientifically valid IQ test available on the web today. Previously offered only to corporations, schools, and in certified professional applications, it is now available to you. In addition to measuring your general IQ, our exclusive test assesses your performance in 13 different areas of intelligence, revealing your key cognizant strengths and weaknesses.". This might seem like a very valid and trustworthy test, but after taking the test, they have you pay to get a certificate sent to you. Since the main purpose of the site obviously is selling these certificates, they want to get as many as possible to buy them. They try to achieve this by giving everyone ridiculously high score, making them believe they are intelligent, forcing them to buy the certificate as proof. Their slogan even is "Smarter than you think".
This is the case of most online IQ tests. They give people with average intelligence a result of maybe 150-170, giving them a rather distorted view of themselves, in which they firmly believe, claiming they "have" an IQ of whatever score they got.
The problem is that the more "official" tests aren't that standardized or consistent either. You may take one test that gives you a score of 107 and then score 117 on another test. The results of IQ tests are also highly dependent on who has previously taken the test as the IQ system is based on the idea that the average IQ should always be 100. This means that if a lot of dumb people take an IQ test, you are more likely to score highly on this test than on other ones. The most valid test measuring cognitive ability I've ever taken is the one they use at the enlistment here. There you don't get an IQ score or anything saying "This is your intelligence". You just get a score, which you can compare to everyone else who has taken the exact same test, which is a large portion of our male population.