I guess it would depend on the area and the type of school to determine whether you should take waiting lists seriously. Say you want a Catholic preschool and there are more students than spots. Then you can expect to be on a list. In our area, there are a few really good preschools that are popular enough to have waiting lists. But there are other equally excellent schools that don't. Oh, and that's a waiting list starting in January for the upcoming school year. Not a 'get your child's name on the list at birth' sort of school.
And run away fast from any place that promises you their's is the essential first step on the way to an ivy league education.
BabyCenter has a good preschool interview form. And I think the February issue of Wondertime has a listing of the most popular preschool styles. Here's another online preschool article at Wondertime.
We did the usual: asked for recommendations, visited schools, asked a lot of questions, watched our daughter interacting with the teachers, etc. We ended up choosing a cooperative preschool. I highly recommend it. You really get to know the families and the kids in your class. You learn about early childhood education. There is a requirement to work in the classroom and help out around the school, but it's not a burden and fairly fun.
Look for texture tables (eg an indoor sand box filled with rice or something), water tables, an art area, outside time every day and an active plan b if the weather is bad, curriculum wide enough to allow for differing interests and abilities, certified teachers, and an insured facility.