North Center is not a huge condo market so there is a great deal of variability in the months of inventory as sales fluctuate. Through a large part of 2009 condo inventory in North Center was running considerably higher than 2008. However, in the early part of 2010 it had improved over the previous year despite higher absolute levels of home inventory. However, as in most Chicago neighborhoods, the months of supply of 2- 3 bedroom condos rose once the tax credit expired. Condo inventory substantially improved throughout 2011 but it's still very high by historic standards.
Meanwhile, the number of days that homes remain on the market has actually drifted up quite a bit over the last 2 years but is still lower than most other areas of Chicago. Recently the market times have matched last year's levels.
Note that the MLS changed their methodology for reporting market times, affecting data since October 2007.