People in tech industry (all I know) tend to call in sick to "recharge" or get things done (that are causing them stress) rather than take vacation. The interesting thing is that this tacitly known to not really be sick and accepted both by peers and management. Vacation == lazy. Sick days == we all pretend we work 60hr weeks non-stop.

Cultural anecdote example from http://maebert.github.io/jrnl/installation.html#quickstart

  2012-03-29 09:00 Called in sick.
  Used the time to clean the house and spent 4h on writing my book.