I reported this some days ago, but it was a rather short report, which might explain why nobody has reacted upon it yet. So this time I'll go into greater detail:

The grid system in columnsets works very well until the moment you include a multiline equation somewhere. This causes the entire rest of the page to be out of alignment with the grid. Try running this code with MkIV:

    \setuplayout
    [grid=yes]
    
    \setupindenting[yes,medium]
    
    \definecolumnset[example][n=2]
    
    \setupformulas[indentnext=auto] 
    
    \starttext
    
    \showgrid
    
    \startcolumnset[example]
    \input knuth
    \input knuth
    \input knuth
    \startformula
    \startmathalignment
    \NC x^2 + y^2 \NC = z^2\NR[+]
    \NC u^2 + v^2 \NC = w^2\NR[+]
    \stopmathalignment
    \stopformula
    \input knuth
    \input knuth
    \input knuth
    \stopcolumnset
    
    \stoptext

A picture of the result can be found in this question on TeX.SE.