I'm not fond of brain teasers either, but small, self-contained questions have value. Often if they're simple enough you can use them in many interviews and establish a base line (if the candidate did a, b or c she will usually work out, if she took route d, that betrays a weakness in X etc).

This is not a replacement for evaluation of a candidate on their own merits, and having a good in-depth technical conversation. But I like having something to ground my evaluations in as well and make them even slightly comparable.

For reference, I do the same thing when I get interviewed; I have a few questions I ask any prospective company so I have some comparative way to evaluate them. Never bad to try to have some metrics in your process.