Another example of the FromMma conversion, from a recent forum post,

convert("Show[Plot[
  Piecewise[{{0, x < -0.5}, {1/5, x < 1.3}, {2/5, x < 1.7}, {3/5, 
     x < 2}, {4/5, x < 2.8}, {1, x > 2.8}}], {x, -2, 5}, 
  Ticks -> {{-0.5, 1.3, 1.7, 2, 2.8}, {1/5, 2/5, 3/5, 4/5, 1}}, 
  PlotStyle -> {Thickness[0.01]}], 
 ListPlot[{{-0.5, 1/5}, {1.3, 2/5}, {1.7, 3/5}, {2, 4/5}, {2.8, 1}}, 
  PlotStyle -> PointSize[0.03]]]",FromMma);

Warning, The options, [Ticks -> [[-.5, 1.3, 1.7, 2, 2.8], 
    [1/5, 2/5, 3/5, 4/5, 1]]], are not translated and 
    are being ignored

  plots[display](plot(Piecewise([[0, x < -0.5], [1/5, x < 1.3],

        [2/5, x < 1.7], [3/5, x < 2], [4/5, x < 2.8], [1, 2.8 < x]]),

        x = -2 .. 5, thickness = [6]), plots[listplot](

        [[-0.5, 1/5], [1.3, 2/5], [1.7, 3/5], [2, 4/5], [2.8, 1]],

        style = POINT, symbol = CIRCLE, symbolsize = [18],

        symbol = [CIRCLE]))

eval(%);

Warning, unable to evaluate the function to numeric values 
    in the region; see the plotting command's help page 
    to ensure the calling sequence is correct

Error, (in plot/options2d) expecting option symbol to be of type 
identical(asterisk,box,cross,circle,diagonalcross,diamond,
    point,solidcircle,solidbox,soliddiamond,solidsphere,
    sphere,default) but received [circle]

Not only (the second) symbol is [circle], but also thickness is [6] and symbolsize is [18]. And the Piecewise conversion is wrong. Ticks are not converted at all.

Alec