Lest you think we are getting collectively smarter, please consider the counter evidence.
If people aren't getting smarter, then the tests must be getting easier. One explanation for the rising scores comes from Ulric Neissner, who argues that the scores are climbing because of the tests' reliance on visual questions, and the familiarity of test subjects with such through the ever-increasing visual world.
Schoolchildren of all ages devote far more time to visual "projects" today than they did a generation ago.
So people aren't smarter across the board, just in those aspects of intelligence that IQ tests find easiest to test.
When talking about the usability of identity systems, you'll often hear somebody say something along the lines of
It has to work for my Mother
the idea being that older web users may have different capabilities with respect to getting around on the Web (or programming the VCR, turning on the flat screen, etc) and that usability of identity systems has to account for these restricted skills (or willingness to learn new ones).
But if Neissner's explanation of the Flynn Effect is correct, then Mom may be a lost cause. Her ability to understand web identity systems through visual cues, without years of early training through video game playing, YouTube browsing, or Viagra spam filtering, is just not there and unlikely to be trainable. Sorry Mom.
With respect to the value of the tests themselves, I think Neissner sums it nicely
no serious scholar claims either that IQ tests measure nothing important or that they measure everything important.