Typically you can treat the output value as a probability.  This is supposed to be the case with a softmax output layer (as is currently recommended for multiclass classifiers) and I believe it should also work with multiple logistic outputs if you normalize the output vector to sum to 1.<p>In my experience sometimes both the decision and the confidence will be wildly wrong (ie. wrong answer with 99% probability) but most of the time this works reasonably well.