Aiko did a very interesting study on code smells - they've compared a number of systems that had been studied previously and evaluated using CK metrics and expert judgements. The new evaluations was based on code smells.
The results are interesting in that sense that code smells are strongly correlated with expert judgements on the quality of the code. This means that code smells can be used as indicators of the well-known "gut feeling" from experts. However, more quantitative.
Very interesting and recommended reading!