I signed for life long membership some years ago, when the sign-in promotion did offer 20'000 miles.

But I never used any Silvwer Wing offer - they are never competitiv for me, and lately (about two years ago) the made it worse for me (I still was a 1K then) cancelling the upgrade possibilities (SWU) on their zone-fare offers and also cancelled the 10% Senior rebates on all tickets.

Not only because of such a bad treatment (cancelling perks like the 10% rebate, that have been promised in writing before) I gave up concentrating my flights on MIleage Plus as frequent traveller program for me, and I also reduced heavily to book flights on UA as long as there are other reasonable flight schedule alternatives (Star-carriers) for me available.