Be careful in comparing what the unit sold for 3 years to what the current list price is. List price really means nothing, it is only closed comparables that hold any water. Therefore, if you really want to get an idea of appreciation, it is best to analyze recently closed comparables in the building.
Furthermore, because we are experiencing a bit of a price decline in the condo market in Chicago, comparing prices from 3 years ago to today's prices may not give you a fully accurate picture. Well, I take that back: It is what it is, so it is accurate in that sense, but if you want to get a long-term picture, you might want to compare closed comps over the past 3 years as a whole, and not just 2004 vs. 2007.
Good luck, the Acorn Lofts are in such a wonderful location!