From Guy Kawasaki's blogpost The Art of Schmoozing:
9. Ask for the return of favors. Good schmoozers give favors. Good schmoozers also return favors. However, great schmoozers ask for the return of favors. You may find this puzzling: Isn't it better to keep someone indebted to you? The answer is no, and this is because keeping someone indebted to you puts undue pressure on your relationship. Any decent person feels guilty and indebted. By asking for, and receiving, a return favor, you clear the decks, relieve the pressure, and set up for a whole new round of give and take. After a few rounds of give and take, you're best friends, and you have mastered the art of schmoozing.