I would like it, if someone goes on holiday, it says how many days, so we know how long we are going to be waiting for...

You can check their profile and it will say when they are going off vacation.

This isn't entirely reliable since some set their vacation to go off a couple days after they return, but then turn it off early.

It also doesn't account for if someone has a second Vacation set that will follow-up the first, ie Vacation March 5-9, then another for March 9-12, then End would show March 9.  At least that's what I see from a quick test, although that scenario is a bit more rare so probably not really a big issue.