Here are some examples to see what one can expect.
The files have all been created under Linux using QWMF and Qt 3.3.3

a) Using the chart example of Qt
- chart_png.png
  PNG export from chart
- chart.wmf
  WMF export from chart using QWMF
- chart.png
  The re-exported WMF file created using PowerPoint under MS Windows
Bugs: The Dense*Pattern style from the cyan section

b) Using QtiPlot, http://soft.proindependent.com/qtiplot.html
- qtiplot_png.png
  As exported with QtiPlot
- qtiplot.wmf
  As exported with QtiPlot
- qtiplot_wmf.png
  And re-exported using PowerPoint
Bugs:
1. Some of the texts are at the wrong position: axes labels, title, legend ("Ca_1")
  and the numbers on the right side of the plot
2. The rectangles seem to be either spurius or at the wrong position
3. The curve is broken (like LineSegments rather than a Polyline)
4. A line is missing at the right scales

[I've not the slightest idea what the reason for this is; implementing clipping
may help with (2) and maybe with (3) and (4), but I'm black regarding offset of
the texts. Any suspicion - and be it only tiny - is highly welcome.]