I've got bitten by a peculiarity of floating point handling recently.
The phenomenon is best illustrated with the following snippet:
$ perl -le'$x=0.05;$y=sqrt($x+$x+$x);$g="$y";print "Is $y equal to $g?
Is 0.387298334620742 equal to 0.387298334620742?
Of course there is nothing surprising here after all. It should just serve as a reminder that floating point numbers are nasty beasts. It is dangerous to have certain assumptions about them. Also, when you write code that processes a lot of numbers then forms decisions based on comparisons ofthem, it is important to check that the code really does what you think it does. Extreme cases, loss of accuracy and so on.