What is "experimental philosophy"? There is, I think, some tension in how philosophers use the term -- tension between a narrow and a wide conception.
Most of the work canonically identified as "experimental philosophy" surveys ordinary people's judgments (or "intuitions") about philosophical concepts, and it does so by soliciting people's responses to questions about hypothetical scenarios. (See, e.g., Knobe's chairman study regarding intentional action, Swain et al.'s study of order effects on knowledge judgments, and Machery et al.'s study of cultural variation in the perceived reference of proper names.) Thus, philosophers sometimes think of "experimental philosophy" as the enterprise of running these sorts of studies. Joshua Alexander, for example, in his 2012 book portrays experimental philosophy as the study of people's philosophical intuitions, as does Timothy Williamson, in his forthcoming critique of the "Experimental Philosophy revolution".
Conceived narrowly in this way, experimental philosophy is a coherent and (mostly) recent movement, with a distinctive methodology and an interrelated network of results. It is possible to discuss and critique it as a unified body.
However, there also seems to be a broader conception of experimental philosophy -- a conception that has never, I think, been adequately articulated, a conception that Josh Knobe and Shaun Nichols, for example, gesture toward in their "Experimental Philosophy Manifesto", before they shift their focus to experimental philosophy in the narrow sense. In this broad sense, philosophers who do empirical work aimed at addressing traditionally philosophical questions are also experimental philosophers, even if they don't survey people about their intuitions. In practice, the narrow/broad distinction hasn't meant too much because almost all of the empirical work of almost all of the people who are canonically recognized as "experimental philosophers" fits within both the narrow and the broad conceptualizations.
My own work, however, tends to fit only within the broad conception, not the narrow (with a couple of recent exceptions). So the difference has personal importance to me, affecting both my and others' conceptualization of my role in the "x-phi" community.
How to articulate the broad conception? Experimental work done by people in philosophy departments seems an odd category, since similar work can be done by people in different departments. Experimental work that addresses traditionally philosophical issues, however, seems far too broad, sweeping in too much research that we would not ordinary conceptualize as philosophical, including physics experiments on the structure of space and time, biological research on the origins of our social roles, and psychological work on the origins of our concepts, since these issues are at the root of philosophy of physics, philosophy of biology, and philosophy of psychology; and sometimes what the most theoretically ambitious physicists, biologists, and psychologists say is not so different from what philosophers of those disciplines say; if by adding experimentation to that, we get experimental philosophers, then most experimental philosophers are employed by science departments.
Here's a thought that is perhaps more satisfactory: Experimental philosophy in the broad sense is empirical research that is thoroughly contextualized within an intimate knowledge of the philosophical literature on which it bears, and which is presented, primarily, as advancing that philosophical literature. (For present purposes, we can define "philosophical literature" sociologically as what is published in philosophy journals and in books classified as philosophy books by academic presses.) This will omit the typical developmental psychologist working on conceptual categories, but probably allow as marginal cases of "experimental philosophers" the most philosophically informed developmental psychologists (such as Alison Gopnik and Susan Carey). It will allow in, as central, work by Shaun Nichols that is not typical intuition-polling x-phi (such as his work on disgust norms and on quantitative history of philosophy). Maybe some of Elisabeth Lloyd's empirical work on the female orgasm will also qualify.
And of course (my main, not-so-secret intention in developing this account) so also will all of my own empirical work. Included, for example, will be my work on the moral behavior of ethics professors, which does tend to be recognized as "experimental philosophy" by the x-phi crowd, despite not fitting the narrow conception; and also my empirical research on consciousness (e.g., here, and chapters 1 and 6 here), which is less often mentioned as x-phi.
But more than that, I think this conception explicitly encourages the thought that a broad range of traditionally philosophical issues can be illuminated by empirical studies, even though they have not yet commonly been approached with the tools of empirical science. For example, empirical research might help illuminate the question of whether philosophical study, over the centuries, tends to progress toward the truth. We might be able to take an experimental approach to the question of whether the external world exists. Questions in the history of philosophy might be approachable by means of the systematic study of citation patterns in philosophical venues. And so forth.
Experimental philosophers, break free! There is so much more to do than just surveying intuitions!
(No accident maybe, that I was a student of Gopnik and Lloyd?)