Does anybody know if these supernodes are paid for by Skype or they're simply users' computers being commandeered by Skype (after getting click-through permission).

The explanation doesn't ring true to me because AFAIK supernodes are used only if a direct P2P path cannot be established between caller and callee.

What we're observing is the inability to sign in and see contacts' status. I always thought that was centralized. Are supernodes involved in signin?