In Feb I joined just to get the (then) enrolment bonus of 10k miles. Paid $220 and received, and have since used, $300 of discount certificates for bookings on .bomb.

Am very happy with Silverwings now I understand which parts of their offering are rubbish. The flat-rate Zone fares, for example, only work on Tuesdays & Wednesdays and don't include tax.

There's also talk of double mileage but none has yet appeared in my account. [Edited: they did after 6 months, the full 12,500 which is the lifetime maximum for SW so no more double miles ever for me.]

Still, paying $220 annually for $300 of coupons seems a reasonable deal.