nested tables

would like to post a topic for discussion and it centers on accessibility
and techique:

when using tables for layout, the cells that contains content may have a
need for forms and data.  the content cell may be inbetween two cells - one
on the left for data and the right for headlines.  there can be a need for
nesting tables within the cell containing the content. for example, if there
is tabular data in a cell, it can use a nested table that may take up one
third or one fourth of the cell height.  

how do assistive devices render a table in a table like this?  what are the
issues?