Marc Andreessen, who sits on the board of both Facebook and outspoken entrepreneur Dalton Caldwell’s Mixed Media Labs (makers of App.net), will step down from Caldwell’s company. On Wednesday, Caldwell blogged about a negative interaction and negotiation with Facebook. Update via TechCrunch: Scott Weiss, another partner at Andreessen Horowitz, will replace Andreessen as a board member. [Source: AllThingsD]