Because I live close to Houston, I am lucky that I can (and usually do) go every day. For those of you who haven't been or may not know, if you sign up for a class at the Houston IQF, you are able to go to preview night and every day at no extra charge. There is a processing fee (last year it was $38) and the cost of the class, but it is totally worth it. You can go to their website and put your name on a list to be notified when the class catalogue is ready to download. Once you have taken a class, you will automatically be on their list as long as you take a class each year. Also, if you sign up for a class, you are permitted to enter preview night at 5pm, where the general public doesn't get to enter until 7pm. Also, there are a couple bag check booths, where you can store your stuff, so you don't have to haul it around. Be sure to take a big bag that you can put it all in, because they charge $1 per bag. You can get your bag and put more stuff in it, but each time you do that, it costs you another $1. There is a parking garage directly across from the George R. Brown Convention Center, and you can also just haul your stuff to your car instead of checking it.
At the Houston show, preview night is always about the vendors for me, because the extra two hours with very little crowding means you can see demos easier and booths are not crowded. I try to visit the special area for "causes", like Alzheimer's, Quilts of Valor, etc., first, then alternate between the quilts and the vendors. Also, plan to stay for Sunday, because a lot of the vendors start marking their stuff down, rather than having to haul it all away. One year, I got 7 packages of king size W&N cotton batting for $100. And last year, I got a small Tutto rolling case for 50% off the retail price.