I was thinking about this question today and then Ian Bogost tweeted a similar question pushing me over the edge into writing about it.
The weakest definition of digital humanities is that all humanities are already digital. What kind of humanistic research or teaching takes place without computers, word processing software, email, database searches, etc? None. But no one believes that definition. No one wants to believe or see that the humanities are already changed and only remediating their historic practices of article and monograph writing.
So the weak definition is one that draws some fuzzy and arbitrary line among digital technologies and says if you use these technologies to study humanistic content then you are a digital humanist. So, for example, Moretti's distant reading practices might be considered digital humanities. I don't know if he thinks of himself as a digital humanist, but certainly the NEH ODH has special funding for humanists trying to work with large data sets. I'm not happy with these kinds of definitions as they don't mark any kind of paradigmatic coherence but simply remark on whether or not one uses the latest technologies. Following this logic one could be a digital humanist one year and then two years later not be, even though one is doing the same work.
Evaluating and using appropriate technologies to conduct one's research doesn't make you a digital humanist; it makes you a responsible scholar. Ignoring available technology or rejecting it out of hand is anti-intellectual. Not that you can consider every new thing either. The point is that as a scholar you act responsibly to the conditions in which you work, including the technological ones.
My strong definition of digital humanities has two main components. There are makers, who build various digital tools for use in humanistic research and teaching. Then there are researchers, who study humanistic aspects of digital media and culture.
Maybe the strong definition is too exclusive though. Maybe digital humanities is looking to grow and be more inviting. In which case I could see adding a third category that would very close to the weak definition: adapters, who are taking emerging technologies and developing new scholarly and pedagogical methods. The difference being that adapters would be see disseminating knowledge about new digital methods and adapted tools as part of their scholarly work rather than simply using the tools to create familiar scholarly products.