Don't know if this was mentioned or not, but it depends on how the pdf was created. If you have Adobe Illustrator, it can save pdf's directly to dwg format. That works, and brings the items into autocad in a somewhat editable format, not the nicest thing, but definitely better than trying to create it from a tiff or jpeg tracing.
A lot of items will some in as splines, but I haven't yet found a way around that.