"Horses for courses," as the British say. I've done everything from walking up to the counter to buy same-day flights and hotel stays, to reserving them 13 months in advance. It depends on the trip. When it seems like finding reasonable accommodations last-minute will be easy I prefer to leave my options open and my schedule flexible. When things need to be booked well in advance to guarantee availability and/or an affordable price, I book as far in advance as needed.