I don't know if you saw my reply to Michael. There is an ongoing genetic study to determine what the origins of the Hourihanes were. I have heard of the Hourihane-O'Brien connection too, but haven't had enough testers to prove or refute this claim.
We are actively recruiting. If you have a male Hourihane relative who can fill in, he knows the geographic origin of your paternal ancestor, to the townland or village, and you/he are willing to share your family tree with the project, please email me: firstname.lastname@example.org
as the project would be interested in funding a 37 marker kit for you.
I have heard stories about County Clare / Dal Cais origin also. Dal Cais is connected with the O'Brien surname. So far, our testing results for Hourihanes in west Cork do not confirm these claims. We are also seeking to recruit Hanrahans in Clare, which can help us test these hypotheses.