I live in Houston and go every year. It is huge. One day will not be enough if you are all quilters. There is just too much to see. The classes are amazing. However, if you are not staying downtown, getting to them is a hassle. Traffic here is crazy and not for the feint of heart.
My advice is: wear comfortable shoes, have a lot of patience and enjoy the experience. I always reserve one day just to look at the quilts and take pictures. Other days are shopping/looking at quilts. I move back and forth depending on where the crowds are (I try to avoid them).
Read the website because there is a lot of good info there. Rolling carts are normally not allowed on the floor and as thimblebug says, watch out for the people in scooters. They'll run into you! Don't be shy about saying "Hey!" or "Ouch" really loud so they know what they've done.
Most quilters are really nice people but unfortunately there are always a few.