it depends - the company used to publish when my birthday was but not when holidays were - i guess if its a company intranet (only available to staff) then its ok
Are you talking about a website where all staff members/public can see your details? We have a system where I work (a section of the internal Intranet) where such details are recorded. However, personal access is limited to senior administrators (who need to update etc). Upcoming holidays would not be covered by the data protection act - many companies do this in a diary format so that other staff can see which weeks are still available.