Hi, I'm the CTO of Sidelines (startup mentioned in the blog post).
For our landing page tests we use Google Analytics which now includes Google Website Optimizer. We track engagement by logging activity time stamps per user in Redis. We also track how many other friends a user invites as a means to measure our k-factor and we are definitely biased towards targeting users that are more likely to be engaged and bring other users to the site.
For our landing page tests we use Google Analytics which now includes Google Website Optimizer. We track engagement by logging activity time stamps per user in Redis. We also track how many other friends a user invites as a means to measure our k-factor and we are definitely biased towards targeting users that are more likely to be engaged and bring other users to the site.