Sometimes reviews in Math Reviews (i.e. MathSciNet) contain a discussion of errors in the paper under review. This can be very helpful: it is a quick way to communicate the nature of the error to the mathematical community, and even to give a brief explanation of how the error can be fixed (when a fix is known). So in situations where a fix can be described succinctly, updating the review seems like a good way to fix the error, especially since (I think) most readers of a paper see this review. Of course this requires some work on the part of the reviewer, if there is one. Does anyone know if this approach is ever used (after the initial posting of the review)?