Since I'm thoroughly confident I won't be getting married before I'm out of school, I'm going to stay as Kathleen Marie McIrish professionally. If somebody in a social circle calls me Kathleen Imaginaryman, I won't mind, but professionally, it will be my McIrish maiden name and nothing else. My parents are paying good money for me to get these degrees and I think they deserve to keep their names on them.
Also, I tend to date guys with really stupid awkward long last names. I think the only way I'd ever change it is if it was like one of my customers last weekend was - her maiden name was O'Irish like mine, but the man she married had an A last name, so now her initials are KMA and she loves it!