Hugely variable. Being married to a teacher, the times we can go away (apart from weekends away, of course) are rather strictly limited (and the most expensive times of year!) But as for deciding how far we want to go, what our flexibility is, how we fit around other things... Hugely variable. I've booked (main) holidays 9 months out, and I've booked holidays 9 days out. I've booked weekends away a few hours out before.

Thanks in part to this site, I've learnt so many tricks about getting redemption availability, cheap flights, cheap accommodation, etc, that I can do so with little quality/price impact. The only variable is where places are in *very* high demand, you need to book early to guarantee being able to get there (although you can always take your chances with late availability opening up if you're flexible). Oh, and visas/medication for more exotic regions.