FORTUNE — Paul Adams is one of Silicon Valley’s most wanted. He’s an intellectually minded product designer with square-framed glasses, a thick Irish accent, and a cult following of passionate techies. As one of Google’s lead social researchers, he helped dream up the big idea behind the company’s new social network, Google+: those flexible circles that let you group friends easily under monikers like “real friends” or “college buddies.” He never got to help bring his concept to consumers, though. In a master talent grab last December, Facebook lured him 10 miles east to Palo Alto to help design social advertisements. On his blog, Adams explained, “Google values technology, not social science.”
In the long history of tech rivalries, rarely has there been a battle as competitive as the raging war between the web’s wonder twins. They will stop at nothing to win over whip-smart folks like Adams, amass eyeballs, and land ad dollars. There’s no public trash talking à la the Oracle (ORCL, Fortune 500) vs. HP (HPQ, Fortune 500) smackdown, nor are the battle lines drawn as clearly as they were when Microsoft (MSFT, Fortune 500) took on Netscape, but the stakes are immense. These companies are fighting to see which of them will determine the future of the web — and the outcome will affect the way we get information, communicate, and buy and sell.