eBay Inc. buys Luxembourg-based Skype Technologies SA for approximately $2.6 billion in up-front cash and eBay stock.

eBay put golden hand-cuffs in place with a further payout of up to $1.5 billion by 2008 or 2009 if financial targets are met. This would mean the whole package could reach $4.1 billion.
Not a bad paycheck for 3 years of work. Niklas Zennström and Janus Friis founded Skype in 2002.

At $2.6 billion eBay pays $48 per user. At $4.1 billion eBay would pay $75 per user. Still ok compared to Dot Com Bubble times. Skype already has 54 million members in 225 countries and territories. Skype is currently adding approximately 150,000 users a day and has created a thriving ecosystem of products, services, developers, and affiliates.
eBay published several documents and a press-release about the deal on their site.