Ads are not the only model for providing free rides. Other Sustainable models exist:
Peer balancining: producers earn free credits for consumption. This is how Internet backbone peering and Team Fortress 2 work.
Freemium, or light users are too cheap to meter, while heavy users pay. This powered Zynga's IPO and many prosumer niches like Photography and web analytics.
Open core with professional services for customization or support (a mix of Freemium and free software). Cloudera.
Peer balancining: producers earn free credits for consumption. This is how Internet backbone peering and Team Fortress 2 work.
Freemium, or light users are too cheap to meter, while heavy users pay. This powered Zynga's IPO and many prosumer niches like Photography and web analytics.
Open core with professional services for customization or support (a mix of Freemium and free software). Cloudera.