I've just finished testing the FalconView GIS Overlay with ArcGIS 9.3 and I'm pleased to say that the testing went off without so much as a bump.
When we moved from ArcGIS 9.1 to 9.2, I found several incompatibilities in the FalconView 4.1 GIS Overlay that prevented FalconView 4.1 from working with ArcGIS 9.2. ESRI had changed the behavior of some of their objects so that we had to rewrite parts of our software to make it work with their new version. In my opinion, this loss of backwards compatibility moving between minor versions was a failure on the part of ESRI software engineering. This time, though, they seem to have gotten everything exactly right. Way to go, ESRI.
I'm very pleased that Georgia Tech will be releasing a version of FalconView 4.1 that is compatible with ArcGIS 9.1, 9.2 and 9.3. FalconView 4.2 will include compatibility with ArcGIS 9.2 and 9.3. For more information on these FalconView enhancements, e-mail me directly.