Few of my readers will be familiar with Wanelo, the social shopping site, because you just aren't in its target market. But Wanelo.com is currently the darling of the dot-com world, or as Bloomberg puts it, "the next big thing in ecommerce". And most importantly to you: they run PostgreSQL.
Last night Wanelo CTO Konstantin Gredeskoul described their "12-step Program for Application Performance" to a packed crowd at their HQ in San Francisco. This is kind of a recipe book for scaling a social web site backed by Postgres. Wanelo's stack includes Rails, PostgreSQL, Joyent, SOLR, Redis, Memcached, Manta, and mobile applications.
Video for the talk is here (sorry about quality, Google Hangouts has ... issues). Konstantin's slides are here.