Ok I'll chime in

I never book ahead.
I always just wing it
That being said...if there's a big event on like a Rally or whatever then I pre book.
My last big trip (the one I'm still posting about) I ran into problems in Billings MT.
I got there about 7pm on a Sunday night.
Couldn't find a room anywhere...they were booked solid.
I wanted to do Beartooth Pass the next day so heading more west on I94 wasn't convenient
I knew there were motels in Red Lodge so I headed that way.
if there were full I would of been screwed.....all is well as they had lots of room.
The next day the owner told me "make sure you start looking for your room for the night no later than 5pm"
summer after all is there busy time of the season
I grab coupon books at rest stops and also use this site
http://hotelcoupons.com/
I got a deal on just about every room I needed on this trip and no room cost me more than $100
I used mom and pops and chains.
It helps to know where your going.
That's why I do so much research in the winter