This is only in regard to academic/research powerhouses and is completely irrelevant for most schools... I am more concerned that you have "done research for ~3 years" and have zero to show from it. Zero publications, zero presentations, zero posters, etc. It may not stop you from interviewing, but that guy on the committee that interviews you and is very research based is going to ask you, "So you spent 3 years 'doing research', why didn't you produce something of substance." Research is important, especially at the top research oriented schools. What you do isn't particularly important, but having a basic feel for scientific method is. But, with anything that you do, whether it be volunteering or research or whatever, we don't want to get the sense that you were showing up, punching a card, washing some dishes and peacing out. Of what benefit is that to your development?