Decided to test some more. Three test-sets:
1. I downgraded (if you can call it that) version 2.1.1 to version 2.0.7 - disbaled all plugins and overwriting all files (except wp-config.php)... After running the upgrade process, still no RTE.
2. Did a clean install of WP 2.0.7 complete with new database and fresh (empty) content. The RTE works like I am used to! Now upgraded that clean install of 2.0.7 to 2.1.1... RTE gone again :(
3. Again a clean install of 2.0.7 (like before with the RTE working fine) and uploaded 2.0.9. Run the upgrade.php process manually because it didn't start up automatically. RTE was still purring like a kitten :)... Then upgraded to 2.1 (upgrade process ran automatically), logged in and went to the Write page. No RTE but the conventional editor so went to Users>Your Profile and checked 'Use the visual editor when writing' because that setting apparantly was changed during upgrade (stange). Then went to Write page: TRE not working!!!
4. Did a clean install of WP 2.1 with clean database: still no RTE, ofcourse...
The strange thing is that I have another WP 2.1.1 installation running on the same server, with TRE! I'm completely at a loss here. Will revert to 2.0.9 untill this is resolved.