Porting Applications from WebSphere to WebLogic?

JFP queries: "I work for a division of a manufacturing company. We're currently running IBM WebSphere 3.5. We are considering a switch to BEA WebLogic 6./7. Has anyone had luck with IBM's upgrade path? Has anyone else ported a WebSphere 3.5 application to WebLogic? If so, how much of code did you have to rewrite? Are there any 'gotcha!'s that you ran into that you would care to pass along?"