Reports that contain "smart measures" will show more columns available in the report definition than are really valid for an actual request. This is an important distinction. Reports that use smart measures (which are typically only those with visitor counts, buyers or recent campaigns) will show that there are 5 visitor measures available (one each for day, week, month, etc). However, when they request report data they will only get ONE of those back, based on the period they provide. For example, if they specify period=2009m01, they will only get the smart measure for monthly visitor count.This makes sense since a monthly count would not be valid for a daily period.