It’s done: My website finally runs under typo3 4.0. It was really hard work, but it’s really worth it. The workspace feature is way cool!
I came across some problems with my mutlilanguage pages. I used the “one-tree-fits-all-languages” concept and templavoila. The only way to define a page in multiple languages with the old templavoila version is to create a translation using the old page module und reference the result in the translated page. (At least this is the way with the least pain, I think.)
With typo3 4.0 those copied references will be marked with a warning saying that there are 2 references to the same content object on the current page. (I guess many people saw this warning.)
The creator of typo3 Kasper Skårhøj has published a very interesting document and a video (http://194.117.233.66/t3dl/why_inheritance_is_bad_for_your_ce.mov) describing a better way (the right way) to define a multilanguage site using the new 1.0.1 version of templavoila.
Finally I fixed some bugs and shortened the URLs of blog posts. The old links will still be functional and will we redirected to the new ones.
