David Sze's notes from when he invested in LinkedIn in August 2004 when they had 900k users:

• Mission. “LinkedIn’s mission is to create the leading, business-focused network site for people where they can “find and contact the people they need, through the people they already trust.”
• Business. “This is inherently a business with strong viral distribution and network effects… And because the whole context of the site is business networking, monetization areas are natural additions to the site, not diversions for users — many of whom at any given time are either looking for jobs, considering looking for jobs, looking to hire people/services/contractors, looking to do sales/BD oriented networking.”
• Path Forward. “Development in three phases: (1) grow the userbase and establish breakaway network effects and scale of user-base/database … ; (2) focus on improving user value, repeat usage, and habit building through (a) better improvements in UI and ease of use, and (b) by building value-added applications and wizards on the database to improve user-mining of value from the network; (3) monetization of the user/network asset through (a) “Opportunities”: …, (b) “InLeads”: …, and (c) “Network Plus”: …
• Monetization. “If the network remains robust, and they succeed in building value and habit, their monetization potential could be a significant portion of the existing Monster.com market as just a first monetization opportunity.”
• Challenge. “My belief (and theirs) is that they have much work to do cleaning up the UI, and packaging relevant applications and wizards on top of their database to surface high-value, simple results matched to the networking processes that people are trying to mine out of the system. I am focused on making sure they get this right before driving too much into mining the user base for money. There is a significant risk in ‘killing the golden goose’ before it’s fully hatched.”
• Scale. “One of the hardest/riskiest parts of this type of business is getting scale on building a large, high-quality user base at reasonable cost — and this is almost fully behind them already.”
• People. “I believe these are our kind of people. Bright, talented, aggressive/competitive, analytical, committed to excellence, hard-working, intellectually honest, and risk-taking.”
• Competition. In those days, Linkedin was one of a bunch of early business-networking startups such as Plaxo, Spoke, Ryze, Zero Degrees, etc. All of these companies were relatively small, though a number were larger than Linkedin.
• Summary. “I am very enthusiastic about this opportunity. I think they are well on the way to being impossible to catch in their space from network development, and they have the potential to build a much more addictive experience on top of that userbase, and to monetize it in ways that are relatively non-jarring to their users, and with large revenues and margin potential. I also think Reid is world-class in this type of business and am excited to work with him.”