They say each app install costs 30c, 10% of installs are active users, and in June 13% of active users were paying members - so the total customer acquisition cost was $23 for each customer paying $4/mo. They expect the percentage of paying people will double in the coming months, although no indication of why that would be the case or what the expected attrition rates are (fitness clientele is notoriously flaky). Unfortunately I couldn't find any Twitter chatter about 8fit so it's hard to gauge the sentiment of the initial 10k users.

Look like a smart investment into a strong founding team, rather than the product itself at this stage (not suggesting that the product cannot stand on it's own merit - only that the "team" slide was the most impressive part to me).