What the appropriate value of the min/max diameter depends on the size of the features you want to capture. You can always estimate the diameter of objects in an image by using the distance tool; in the module display window for IdentifyPrimaryObjects (or by double-clicking the file in the File panel on the bottom-left of CellProfiler), select Tools > Measure length, then click on the image and drag to create a line. The length of the line segment is shown in the bottom-right of the display window.
If you do this for a few objects in the image for a given magnification, you can get a sense of what the min/max diameter should be.
Also, I'm attaching an adjusted version of the pipeline above, which I think should work better for the example image you posted. Basically, I manually adjusted the smoothing filter size and the maxima suppression distance, as well as changed the thresholding method used.
2012_11_06.cp (4.12 KB)