12 Balls, 1 slightly heavier

I got asked this question at least in 3 different job interviews!  What's the point?  What are they "looking" for?

At least the next 2 times, I already had the answer and just spewed it out.

The question:

You have 12 identical balls but one slightly heavier.  You also have a balance scale.  How would you isolate the slightly heavier ball using the balance scale as little as possible?

Answer:

Divide the balls into 2 groups of 6.  Use the balance scale to find the slightly heavier group and discard the lighter one.  Then divide the remaining 6 into 2 groups of 3 and weight on the scale.  Discard the lighter 3 balls.  Now take 2 of the remaining 3 balls and compare them on the scale.  If they weight the same, then the left over one is heavier.  If there's a difference, then take the heavier one on the scale.

>>9
yes, the standard trick is to use a binary search
However, I have heard it claimed that (with 12 balls total) you can find the odd ball out using only 3 weighings, if you don't know the odd ball is heavier/lighter.  I heard this a long time ago, and haven't put enough thought into it.  It's probably not as hard as I'm making it out to be.  The puzzle you suggested is interesting.