What I like about all of these YC Facelift's are the call to action buttons. They all have a very predominate button to get people using/purchasing/signing up for the app. They also have very clear descriptions/videos of what the product does, examples and testimonials.

They do exactly what the homepage of a product needs to do... sell the product. Make it clear what the product is and easy to do == increased sales/conversions/signups.