I teach a writing class at my local community college and got a question from a student -- would an agent consider representing someone based on a self-published novel? Should the student mention that what they're submitting has been self-published? My immediate answer to the student was no, but then they said that it's sold pretty well. Does that make a difference?
The unwritten "rule" (though some have written it) is that a self-published book should have earned at least 3000 copies on its own steam to be considered a "success." I don't know where the number came from, but I've heard it many, many times and read it on agents' websites. So no, if it's below that, don't count it as a publishing credit and don't mention it.
However, we're seeing more and more people who self-published their novel first, then were shocked to find out how little they sell and how costly the process is (usually for the readers, because the books are a little more pricey than mass-produced books), decide they want to get published traditionally. If you're pitching a manuscript to us, and for some reason you want to send it book form ("I had it printed by Authorhouse), we're not going to be doing a lot of complaining. It's one of those things that doesn't help and doesn't hurt.