You betcha! I've been planning my Paris trip since March and won't be travelling until November. If I pay say, $700 for a ticket to someplace and suddenly they have a sale where it goes down to $200, I'll just reissue it and spend the $100 to change it, I'm still saving money! As for cars and hotels however, that usually waits until about a month or so out. Unless I'm going to an Olympics where I plan ahead by years (lookout Vancouver!!!).

And as for planning things to do on my trip, I just read up on the area and decide what I want to do, then play it by ear once I get there with a list of things to do. No sense in committing yourself day by day, things can change so quickly (ie the weather, your health etc etc).