Since the site is being re-written, and since there has been many requests to change the way new vacation days are added in the beginning of the year, how about something like "number of vacation days given = 1 / (number months not online + 1)".
Since vacation days are added, on the 1st January, this means that if the player has been online on December he would get 1/(0+1) (all) of the vacation days heis allowed to, if he has not been online on December, but has logged in on November he would get 1/ (1+1) = 1/2 of the vacation days he is allowed to, and so on...
This would mean that if a person hasn't been online for a year, and he is a black rook, he would get about 8% of the vacation days he is allowed (4 days to be exactly), instead of the 45 days he gets now.
Of course there should be a way to give the rest of the vacation days to that player if he ever logged in again.