Negative results vary from field to field. In math or physics, a conclusive negative can be very important in deciding what to study next or disproving established theory. In biology, a negative usually just means "I haven't found what I'm looking for yet".

And that is the exact problem with certain researchers. I just had to explain this to my undergrad who's project resulted in negative results (his 1'st study). I congratulated him, as he discovered that the treatment he gave did NOT effect the genes he looked into. He didn't understand, so I had to explain that his study (with the correct controls), provided information that is useful to science. Negative data = data. Data = good :)