Ugh. I'm not trying to be super negative, but he's setting a bad precedent by taking half the amount of allowed leave. "We offer 4 months, but Zuck only took 2. Wanna be like Zuck?" He should take the full 4 months and show everyone that it's OK. This is like the unspoken mantra of "unlimited vacation" really being only 2 - 2.5 weeks.
I think it depends on your company and management chain. When I worked at Netflix I took more vacation than every before. I'm not even sure how much, since it was untracked, but definitely more than 4 weeks a year.
Our management made sure to set a good example by taking plenty of vacation.