Sitting especially pretty will be the firms that backed Twitter. Menlo Park's Benchmark Capital, for instance, owns a nearly 6 percent stake, according to regulatory documents  now good for $1.3 billion. Kleiner Perkins Caufield & Byers, which one person familiar with the matter said invested close to $150 million in Twitter at the end of 2011, probably saw that stake shoot past $1 billion as well, based on the company's rumored valuation when Kleiner invested.