Do you mean if you purchase more than one seat?
IIRC, a person purchasing two seats for themselves can get 2x redeemable miles (I think I've seen this posted before), but only 1x MQMs.
EDIT:
http://www.flyertalk.com/forum/delta...ne-person.html seems to continue the debate of whether or not RDMs are earned on the second seat...anyone have any thoughts?