Read the release nots of all major releases between 8.2 and 9.1, but most of all, test your application well.
Our application has moved from Pg 7.1 thru various releases over the years to the current 9.2. The implicit cast issue and the default representation of bytea columns are the only thing that have required our application to change.
Any reason you're not moving to 9.2 instead of 9.1?
