Addthis and Sharethis provide free social sharing services, but the problem is that the cost turns out to be you letting them drop any number of pixels on your users for different advertising networks. This is a great description of the discovery process this guy went through to figure it out. not really free, also known as "comes with externalities". jk.
slides are a pitfall in general since way overused, but these ones are good. I think they have some advice that's pretty right on based on the last 5 years running a startup, especially on the recruiting front.