Always match! I can't stand the feeling of two different socks on my feet!
It gets worse. All of my socks; sport, ankle, black, navy, tan, brown and grey are from the same company. Further more I can't even wear the same colour socks from different product cycles. eg. A 2 year old black sock won't go with a 1 year old black sock because they've faded different amounts. Finally, I always try to match my socks to my dress pants!
I'll wear ripped sweat pants and a tie die t-shirt to Safeway, the mall or even the bar... but when it comes to dress clothes I'm full on OCD...