I do find personality testing things quite fascinating in a 'but I don't put too much faith in them kind of way'. According to Personal DNA (how could I resist a title like that?!) I'm a considerate analyst. The different coloured blocks (see below) represent the degree to which certain traits apply. Thus, scrolling over them tells you I have, apparently, 'low spontaneity', 'slightly low femininity', 'average masculinity', and 'average confidence'. None of those surprise me particularly, but I don't know what people who know me would make of it.
I came across another test via a science site the other day that tries to assess the extent to which your character resembles that of someone with some degree of Asperger's syndrome. Starting from the premise that scientists/geeks seem to have an inclination towards that direction.
The results to this one don't come in a pretty chart but were quite interesting, yet unsurprising, nonetheless. I scored 22, which ranks me below 'Average Math contest winner'(24) but higher than Average male or female computer scientist (21), Average male scientist, and average male or female physicist (19) Average man (18) Average female scientist (17) Average woman, and average male or female biologist (15).
So essentially, neither of these results told me an awful lot about myself that I hadn't already surmised, although I do think of myself as being fairly self aware, which is a trait in itself. I guess these sort of things could be useful (other than in a procrastination capacity) if you felt you didn't know a lot about yourself, or had changed a lot (I know I would have answered some questions rather differently a few years ago), but these sort of things only take a snapshot of a person outside of the context of some of their environment. Essentially, I think if you like the results one can say, 'How true', and if not, then happily take them with a pinch of salt! Who a person is will never be completely uncovered by a quiz, and I think it's important to define oneself by a number of other things...