Haven't had much luck offloading your older Surface to help pay for a Surface 3? Microsoft thinks it can help. Similar to its Surface Pro-oriented effort from a few months ago, it's launching a US trade-in program that will give you up to $150 toward a Surface 3 if you turn in a Surface RT or Surface 2. The discount likely won't compare to what you'll get if you drive a hard bargain on Craigslist or eBay, but it's guaranteed cash -- if you're only concerned with upgrading to the latest tablet as painlessly as possible, it might do the trick. Just be sure to decide quickly, since you have to give up your old device by May 31st.