I was part of the early days of Lotus Notes (1989-1996) while at Price Waterhouse. I worked with Sheldon and his team and then later worked for him at a start-up. There is a great podcast interview with Sheldon Laube linked to from this article, it is very relevant to the conversation today around enterprise collaboration and social interaction.
Enterprise Collaboration/social interaction is almost a back to the future moment. We had it with Lotus Notes and now people are starting to recognize again the power of collaboration.