Have you ever taken a personality quiz/test that helped you have valuable insights? If so, what were the tests and how were they useful?
The only useful ones I've found all yielded the same type of insight. They showed me where I stand relative to others, which is can be genuinely useful since representative samples of large populations can be hard to come by. This includes IQ tests and tests for mental disorders (in my experience, people are usually aware that they are, for example, smarter than the average (although the Dunning-Kruger effect might complicate this) or have some intrusive thoughts and compulsive rituals, but might be surprised to find that they are three standard deviations above the norm or that their symptoms are sufficiently severe to be considered OCD).
No remotely reliable (as in, not astrology) test I have ever seen has revealed genuinely surprising information for a moderately self-aware person, outside of ranking. Furthermore, they rarely gather personality data in a remotely subtle or non-transparent way ("do you like spending lots of time with large groups of people?" "yes..." "surprise, you're an extrovert!"), and thus seem super susceptible to test-takers' attempts to confirm a desired identity.
An example of a more interesting/subtle way to potentially conduct a personality test would be to use question like OKTrends' "do you like beer?" which clusters strongly with "do you have sex on the first date," and, potentially, sexual openness. Such results might be harder for manipulate (consciously or unconsciously) and could assist with deeper self-awareness.
Edited because the first link was broken.
Regarding your thought about subtle personality tests: I find the attachment styles model a fairly powerful predictor of personality, and particularly suitable for dating. It seems to me that people fall into one of the four attachment styles quite reliably, it is fairly easy to know which one and the correlates of each style are easy to remember.
This is interesting, thanks for the link. The model seems to be partly based on one's assessment of self-worth as compared to their partner. Based on this I'd expect to see a person exhibit different styles depending on who they're dating, though this effect could be diminished by acclimation. This might account for some portion of the 20-30% of people who change styles. Is this explored in the literature? Or maybe I'm misunderstanding and the self- and other-assessments are purely positive or negative and not at all comparative.
Also I tried searching for ... (read more)