After sttudying the sources and a bunch of trial and errors I can come up with the following solution which works for a two solumns set!
Great. This works. Now for something different. While learning ConTeXt, I find that often the syntax escapes me. Take for instance:
\definecolumnset[example][n=2]
\define[1]\MargText{% \ifodd\mofcolumns{% \inleft{#1}} \else {\inright{#1}}\fi}
\starttext \startcolumnset[example]
\MargText{Here left of column}
\input tufte
\column[local]
What does [local] mean here? According the the manual one should say \column and I can't find the explanation of what local means or what you are doing here.
The example definition of a columnset presented above is copied from the manual "Columns". - Often commands take optional arguments. Porbably this would also work without the [local]. Willi