Incompatibilities between KOMA-Script and titlesec

I've never used this combination myself, but a search with your favorite engine should show you that there are some incompatibilities, e.g. (all in German):

• Paket titlesec und KOMA-Skript-Befehl \setindexpreamble (it was originally a usenet post, but the archived Google groups version is broken; with an interesting answer of Markus Kohm, the author of KOMA-Script)

• \setpartpreamble funktioniert nicht mit titlesec?!

• titlesec und scrpage 2 (on Markus Kohm's website with answer of him)

• Abstand Gliederungsziffer <-> Überschrift (again on komascript.de)

• Paket titlesec und \dictum aus KOMA-Script

• Platz vor und nach Sections anpassen (again on Markus Kohm's website with answer of him)

See this answer of mine for an additional observed incompatibility: Can't shift/position \chapter with titlesec?.

Update in beginning of 2014

With recently published version 3.12 of KOMA-Script one will get a warning when compiling a document with titlesec:

Class scrartcl Warning: Usage of package `titlesec' together
(scrartcl)              with a KOMA-Script class is not recommended.
(scrartcl)              I'd suggest to use the package only
(scrartcl)              if you really need it, because it breaks several
(scrartcl)              KOMA-Script features, i.e., option `headings' and
(scrartcl)              the extended optional argument of the section
(scrartcl)              commands .

The KOMA-Script classes provide the commands \addpart, \addchap, and \addsec which will start a new unnumbered part/chapter/section that is nevertheless added to the ToC. If you combine KOMA-Script, titlesec, and hyperref, be sure to add a \phantomsection in the after argument of a \section redefined with \titleformat -- otherwise, the ToC links of \addsec will point to the wrong page.

\documentclass{scrartcl}

\usepackage{titlesec}
% Incorrect ToC link to \addsec
% \titleformat{\section}{\Huge\sffamily}{\thesection}{0.5em}{}
% Correct ToC link to \addsec
\titleformat{\section}{\Huge\sffamily}{\thesection}{0.5em}{\phantomsection}

\usepackage{hyperref}

\begin{document}

\tableofcontents

\clearpage

\section{foo}

\clearpage

\addsec{bar}

\end{document}

Currently, titlesec (in version 2.10.1) is fully incompatible with KOMA script. The following minimal example doesn't even compile anymore:

\documentclass{scrartcl}
\usepackage{titlesec}

\begin{document}
  \section{one}
\end{document}

My system shows the following errors:

! Missing number, treated as zero.
<to be read again> 
                   }
l.5   \section{one}

? 
! Illegal unit of measure (pt inserted).
<to be read again> 
                   }
l.5   \section{one}

? 
! Missing number, treated as zero.
<to be read again> 
                   }
l.5   \section{one}

? 
! Illegal unit of measure (pt inserted).
<to be read again> 
                   }
l.5   \section{one}

?