Todd Carlisle, director of staffing at Google, told a panel at the Inforum conference...that no job applicants ask about work perks, and no one turns down a job based on what perks are available.
It is possible that no applicants need to ask because they are already familiar with the perks Google offers. I recently turned down a very generous job offer when I found out the hours were very rigid and the dress code strictly enforced.
I wish there were a site like Glassdoor that detailed the perks offered at various companies. I'd like to know upfront what the dress code is, what hours employees are expected to work, how many vacation and sick days are offered, what holidays are observed, what the 401k match is, and what health insurance plans there are, etc.