Microsoft took nearly three decades to grow to 75,000 people, while Google has become a very large company in a fraction of that time.
"They are trying to double in a year," Ballmer told a crowd of Stanford Graduate School of Business students on Thursday. "That's insane in my opinion."
But, he added, "it doesn't mean they won't do it well."
Video: Ballmer sees Google's model as unproven
Says Google is still in an early phase, in which it can milk its "one good idea."
There are advantages to the deliberate management structure that Microsoft has put in place, he said, adding that he isn't sure anyone has proven "that a random collection of people doing their own thing" has created value. Among Google's perks, the company is widely known for letting its engineers devote 20 percent of their work time to pet projects.
As in the past, he characterized Google as a one-trick pony, playing down the company's efforts beyond search.
"They do a lot of cute things," Ballmer said, to huge laughs from the business students.
"We do a lot of cute things too," he said. "We have a robotics effort."
Although not in the audience for Ballmer's chat, Google CEO Eric Schmidt happened to be not far away, eating lunch at the business school cafeteria as Ballmer's chat began. Schmidt teaches a class at Stanford's business school.
At Stanford and schools throughout the country, Google and Microsoft have emerged as each other's fiercest rivals for talent. Ballmer, who attended one year of the two year Stanford Business School program, makes fairly regular stops here, having
Ballmer said there are basically four stages in business: coming up with an idea, getting it to critical mass, milking it financially and then finding a new idea.
"Google is in the part of the cycle where they are milking," Ballmer said, acknowledging that's a fun stage. "That was the '90s for us...or I would say the '80s and '90s."
