We heartily recommend a look at the website of Dr. Tyrone Bowes. He is a Dublin-born scientist with a remarkable grasp of the interaction of DNA with family groupings and history/geography. We believe a look at his site at http://www.irishorigenes.com/ will be very educational.
He carries out a remarkable number of lectures throughout Ireland and abroad, and pinpoints detail about family areas that can be very revealing!
He also maintains a site on facebook at http://www.facebook.com/IrishOrigenes