From Mike Boyd’s weekly update:
7,100+
Based on an independent Airports:USA analysis, the number of overlapping markets technically represented by the merger of Delta and Northwest, defined as city pairs where a consumer can possibly book either carrier.14
Out of the top 100 overlapping markets, the number (other than routes connecting existing DL/NW hubs) where the combined market share of the new carrier will increase by more than 2 percentage points. The majority are under 1%.0
As of today, the number of airports where combining Delta and Northwest will result in single-carrier monopoly service.
Evan Sparks's Aviation Policy Blog 
One number I wish we had the information for. How many mileages points the frequent fliers have, and how many miles may be lost with the merge.