Today is a milestone day for Microsoft, and time will tell whether it will be a milestone day for search marketing. The MSN adCenter opens for business today, inviting applications for beta participation. Judging from detailed descriptions and screen shots at the site, MSN adCenter seems to operate without much variation from models established by Google AdWords and Overture (now Yahoo! Search Marketing). I suppose, in this arena, innovation would merely confuse advertisers who already feel stressed at having to operate multiple campaigns with multiple service providers as the market fragments.

One important difference, though—the differentiator—is demographic targeting offered by MSN adCenter. AdWords and Y!SM provide geo-targeting and various keyword exclusion operators, but Microsoft is providing "target bids" based on age, gender, time of day, and day of week. An example:

Base bid: $1.00 for "car"
Target bid 1: $0.10 for male
Target bid 2: $0.10 for ages 18-25
Target bid 3: $0.20 Monday through Thursday
Target bid 4: $0.10 6 p.m. to 11 p.m.
Total bid: $1.50

As John Battelle notes, traffic volume is one key to success. But for now, I imagine Microsoft just wants to ensure that the system works as advertised; hence the cautious rollout.