I'm very surprised at the positive response here. I agree this is consumer friendly, but for those that are frequent united travelers(likely most of the posters here), it has a lot of disadvantages:
1) Less availability for award seats as more people will be able/want to use miles that previously would be worthless
2) Less breakage of UA miles(miles cost UA more) and therefore we can expect accelerated devaluation of the miles
3) More people will get the UA credit card, increasing the number of outstanding miles/liability and therefore we can expect accelerated devaluation of the miles
If awards are not harder to book and/or miles devalued the extra cost to UA will be very large. I doubt UA is planning extra expense for this feature. We (as in those that fly UA frequently or know to do a token transaction) would be better off with expiring miles.