I am urgently looking for a component to track employee leave. There is no such component available for Joomla and I think a lot of companies would want this for their intranet.
This could be perfectly combined with Community Builder in my opinion.
Have you looked at the numerous calender components that are available for Joomla? They may not be designed exactly for this, but it is possible to record vacations and other absence as multi-day entries in a calendar.
A simple way is to just define a text field in the CB profile and let the users input the vacation dates.