I think I'm going to do this. I have a business trip (from DFW) to SFO planned for 1/21 - 1/23 (need to be there the full day of 1/22), which would cost me $220 for 3000 miles. I can extend my return an extra day and piggyback a SFO-PHL-JAX-CLT-SFO into it for an extra $225 and get another 6000 miles. I'm tempted to do two of those to hit Platinum, but (depending on whether sub-500 mile segments count in the challenge or not), I might be a few miles short and I doubt there's as much of a difference between Gold and Platinum as there is between Silver and Gold. If anyone has cheaper idea for a MR (on US metal for the challenge), preferably domestically so I have a chance of upgrades, let me know.