Here is an article by RHF on water changes:
http://reefkeeping.com/issues/2005-10/rhf/
I think the summary is that the difference between doing 1 30% water change vs 30 1% water changes is about 5% (it's been a while since I read it, don't recall the exact number) in terms of nutrient export. He argues that frequent small changes are easier to do, remove the need to heat the new water, and help keep parameters more stable than less frequent large changes.