This is precisely what I have done-I graduated from college in May. Got the NW WP Visa, went to Chile for free to visit my gf this summer (now I dont use NW for miles/never used the credit card). Used some existing miles I had been saving up on United to go to Europe with UA/Star Alliance for free. Now I have about 60k with United, and by the end of the year Ill have about 110k on Delta and will prolly be Silver (Im working in France right now, so Ive been trying to take advantage of as many cheap trips back to the US as possible). As a student and still now, I have always bought the cheapest fare regardless of the airline. Usually this contributes to my UA or DL balances, but I would rather take twice as long to get a free ticket on two airlines than pay more and get one free ticket quicker on one airline.