I skipped pre-algebra and had no problems. In my day, the 5 or so best math students in the 7th grade skipped 8th grade math/pre-algebra and went directly to algebra. It was a school policy.
DS11 also skipped it/kind of did a bit of it with me when he was pretty young. No issues with him either.
From what I've seen, pre-algebra is basically algebra light (lots of solving for variables in basic equations, for example). It's a slow introduction to algebra. IMO, it's very useful for kids who aren't really mathematically inclined, because if they do well in this course, they will be well-prepared for real algebra. Nowadays, schools seem to be in a hurry to rush students into algebra without, in many cases, adequate preparation.
