http://shopping.usairways.com/en-US/...haremiles.html
If I understand correctly, share miles give better value.
you share 50000 with someone else, u lose 50000, they gain 100000, net gain 50000. cost =50000*.01*0.075+30=567.5. Then ask ur friends or relative transfer miles back to u, u will get another 50K bonus for 567.5. total bonus 100K=1135.
For buying miles 50000+50000 bonus=50000*.025*.075+30=1373.75