Staff Holidays - Planning

Are there any plans to allow holidays to be set against a resource, which would ultimately affect the planning on projects?

Administrative projects are done for this.
For instance, you create a project "Out duty" with project type "Administrative".
Then add activities to this project such as : "holidays", "sickness", ...

At this step, any resource can enter real work on these new tasks : no need to affect resources to the project, nor assign them to the activities.
Then, holidays are just entered as "real work" in the future.

This will forbid the planning to try and plan some work for the resource on these off days.

The holidays is a reality that cannot be "forgotten" in a tool of project mangement.

They are not forgotten : administrative projects are dedicated to them
... and all the others "off" days, such as sickness, training, ...

All the activities depend on presence of resources

Yes, and I continue to think that allocating real work for off periods is the best way to manage this.

in the calendar, at the step of planning, the days signaled as "Holidays"

Not in the existing calendar as it is just a global overview of off days, for everyone.
But the idea to input the off days by just clicking on some calendar view could be an interesting improvement.
Ticket #1166 recorded.
Now, this improvement must be able to :
- select the administrative tasks corresponding to the off day
- give the possibility to select 1/2 days (or else)

a message like "impossible to plan this ressource because of holidays from 01/08/2013 until the 25/08/2012 "

I don't understand where you expect the message.
To my opinion there is no difference with a resource busy because already assigned to a task and a resource out of work.

regards.