As for the 0.5% conversation ratio Binary_Moon suggested I have to say that is a terrible conversation ratio and well below marketting standards (1% untargetted, 2% targetted). If that's all you get in shareware demo/purchase conversions there's something wrong with your product, sorry.
Nope, 0.5% is good, forget what you read in all these bloggs and ramblings on sites such as Dexterity.com, this is real life, we sell our software we are talking from experience!! The chap from Binary Moon works for the worlds largest portal, he knows his stuff.Please get your facts right when you are advising this guy.