A famous hedge fund manager has made a big bet on Starbucks stock. : Shares of Starbucks (NASDAQ: SBUX) surged earlier this week, after activist investor Bill Ackman touted the Seattle-based coffee titan at an investment conference. Ackman's Pershing Square hedge fund recently accumulated a roughly 1.1% stake in the company, currently worth more than $800 million. In his recent presentation, Ackman predicted that Starbucks stock could roughly double within three years. That projection is probably too ambitious. Nevertheless, the shares do have a ton of upside, particularly for long-term investors.