What is the difference between a $14 gallon of paint and a $30 gallon of paint.

Aside from $16 that is. :)

Discounting designer textures and the sort, is there a real difference in the qualities of paint enough to make one worth spending twice as much on?

It usually boils down to coverage, a more expensive paint will have more pigment rather than carrier so it hides better with one coat. I would be suspicious of a $14 gallon of paint. Benjamin Moore paint is my personal favorite and it runs $35 per gallon.

Thanks Steve, you will enjoy reading this. Is Walmart Paint Quality Paint? (http://www.thriftyfun.com/tf73529969.tip.html) Looks like Walmart paint is thin Sherwin Williams paint.