After updating to 0.9.2 I noticed that /w3tc-[domain]/min/.htaccess and /w3tc-[domain]/pgcache/.htaccess contained the rules of both the old and the new version. The rewrite rules of the new version are simply appended to the old rules.
After fixing that I still got 500 errors when I tried to open any of the w3 total cache setting pages. To fix this problem I had to delete the settings file w3-total-cache-config-[domain].php
To mimic the situation of a clean install I also removed the W3TC info from the root .htaccess file.
After that W3TC was running in basic mode.
The 500 errors reoccurred when I tried to modify the root .htaccess file to add rules for disk caching. The only way to solve that problem was by commenting out the last rewrite rule of the W3TC Page Cache core:
# RewriteRule .* "/wp-content/w3tc-%{ENV:W3TC_DOMAIN}/pgcache/%{REQUEST_URI}/_index%{ENV:W3TC_UA}%{ENV:W3TC_REF}%{ENV:W3TC_SSL}.html%{ENV:W3TC_ENC}" [L]
That disables the page cache, so it is not a real solution.
It seems this version has some serious bugs, which is a pity because there are some really nice new features in this version.