How do you calculate Cost of Customer Acquisition if your dev team does all sales & marketing?

Having each employee track how many hours go into production and how many go into sales/marketing is the easy answer. In reality, it can be very hard to keep a team of people that accountable, and anyone you show those numbers to will be a little skeptical. On top of that, I would think you run a high risk of losing time to task switching when the same individuals are in charge of production and sales.

Instead I would try to find a specific member of the development team to be in charge of supporting sales and marketing. Then you could either track that one individuals time distribution or every month or so make an estimate for how much time that one employee helped sales/marketing. Helping with demos seems fine, but I would be concerned about efficiency if my programmers were worried about responding to potential client emails. Salesmen/saleswomen are just able to stay more focused and give better attention to a prospective client while including the tech-ies only when necessary.

There are tons of tools out there for tracking time. Some free, some cheap. Personally I use Redmine but it is just one of many.