Add Larry Summers to those worrying about a 1999-style internet bubble after LinkedIn's (LNKD)...

Add Larry Summers to those worrying about a 1999-style internet bubble after LinkedIn's (LNKD) exuberant IPO, but Dealbook believes this boom is different. The companies going public now have more than just “eyeballs” - they're real businesses with real earnings and revenue - and there's no flood of new companies coming to market.