When using the GDAL plugin, "Polygonize (raster to vector)" any values in the resulting vector layer is truncated to integer.
I have a raster showing windspeeds in squares of 500*500 meters, in the metadata-field i read that the lowest value is 2.5899999142 and the highest value is 12.6599998474. Then when polygonizeing, the result layer only has values: 0, 1, 2, 3... and so on. No decimals.
I have googled the issue and found this: http://trac.osgeo.org/postgis/ticket/650 Don't know if it helps though.