GIS (ESRI), Autocad and Microstation user as well as a (GIS/GPS) Systems Analyst for the Texas Department of Transportation. I firmly believe that the big 3 mentioned before should be fully interoperable and the other 2 fall under the category of GIS's in their own right. It's not uncommon in this business to use all 3 in 1 project to progress forward to the achievment of your final product. Taking on more of a developmental role with TxDOT and beging to use AGS Server and Image Server to provide web based maps and aerial imagery for public consumption as well as for internal department use.