I have tested the compatibility of 8.2 and 9.0 completely, as my organization is undergoing the migration from 8.2 to 9.0.
Following are the findings:
1. 8.2 client is able to connect to 9.0 server, but no of the qvw scripts on the server can be seen. (no access right control etc)
2. 9.0 client is able to connect to 8.2 server and open any qvw deployed on 8.2 server.
3. the rest of features are fully compatible, i.e. qv scripts, basic biff/html export funtions and pdf printing with QlikviewPDF in 9.0
hope the above info will help.
I have already done the migration.
The issue about viewing QV script on server is due to the access right set up problem.
In general, the migration was quite smooth.
Just like normal microsoft product upgrade, run the qlikview exe application, it will inform you that old version is existing(server) and help you to remove it before install new one.
For Qv.exe, you may install to same dir to overwrite it.
Uninstall original QV & install new version.
It seems that the configuration details are in registry, therefore, no additional configuration required after installing new QV server.
However, those additional features compared to earlier version are still require configuration.
No new plug-in installed for my users. Seems that Version 9 and onward server is built-in with plug-in features.
It is transparent to my users, they can still use old client to connect to new server. (my migration is server migration 1st, then user clients).