That's what several major Web sites learned Tuesday afternoon when a power outage in downtown San Francisco disabled 365 Main , a Web server company that hosts sites including Craigslist, Technorati, SixApart, Yelp, GameSpot, the homepage of Sun Microsystems (nyse: SUN - news - people ) and Red Envelope.

FORBES: Blackout On The Web

Rackspace has agreed to buy Mailgun, a San Francisco-based startup that provides e-mail server tools.

FORBES: Rackspace To Buy Mailgun

Microsoft CEO Steve Ballmer will officially unveil Mobile Server during his keynote address at the company's Enterprise 2000 event in San Francisco.

CNN: Microsoft introduces wireless server