Become a better programmer by taking a shower

One is that (IMO, anyway) it's the very, very rare individual who can actually get through them by thinking their way through them. The interviewee either knows the answer outright, or they don't. So the interview becomes more, "how many of these brainteasers have you seen before?" Yeah, you can gauge a LITTLE bit about a person by seeing how far you have to lead them to the answer before they get it, but not much.

Another is that the interviewer is not trained in whatever black art it is that can "get an idea about the candidate's thought process". And then, what if you can? What does that matter? Can the guy do the job, or not?

All these questions do is waste time, attempt to give the interviewee a false sense of the company's cool factor or exclusivity, and find out how many brainteaser or "I interviewed at <company>..." blogs he's read.

You know, sometimes, personal hygiene gets ranked not to high on the to-do list :)