The culture at Google is very much like the old culture at Microsoft – back when the company felt like most employees were in their mid 20’s. These kids don’t have a life yet so they spend all of their time at work. Google provides nearly everything these people need from clothes (new T-shirts are placed in bins for people to grab *twice* a week!) to food – three, free, all-you-can-eat meals a day. Plus on-site health care, dental care, laundry service, gym, etc. Imagine going from college to this environment and you can see how much everyone works. People are generally in the building between 10am and about 6pm every day, but nearly everyone is on e-mail 24/7 and most people spend most of their evenings working from home.
This culture changes a bit with more experienced folks. They generally work 10a – 6pm like the new hires, and most of them are on email until around midnight. It’s pretty common for them to be working most of the evening, too.