Further to my earlier post about PrimoPDF, I repeated the process on the same file but having installed PDFCreator. I experienced exactly the same result. At this point I wondered if it was a screen issue rather than a software issue. Bottom line is, it was. The hard copy is fine and when zoomed into the document in Acrobat at 1200%, the staff lines are completely evenly weighted - they just look horrible on screen at any 'normal' resolution.

There is little to choose between PrimoPDF and PDFCreator at all but for ease of use I think PrimoPDF has the edge - not by a lot but it does. PDFCreator is potentially slightly more powerful and gives you slightly more options at output time but for the vast majority of users I think PrimoPDF would be preferable for its simplicity (without appearing to compromise power).