Originally I thought that absolute pixel positioning would be the right way to go for a one-off design, but when I was looking at the exercises I changed my mind. For example my first round, there was a left column with a 3x3 grid, and a right column with some info spelled out on it. The easiest foolproof way that I had to make a 3x3 grid would be to use a <table>, and then I can make both columns floating <div>s, so I went with it. I made the width 30% because I didn’t want to overestimate the width or height of anything.
Overall I think most sites were close to correct, but small changes in color or a bad background-image can really kill you.