Free Convert Visitors with Google Analytics
Banner Ads for paid links from Your Directory on SEO Sites
It's like waving a flag with a voice-activated, wind powered speaker that yells "ban me! ban me!" Sure, you might get clicks and money and submissions, but you've gotta know that search quality team members read SEO blogs, too - so if you do this, make sure your directory is ready to be manually reviewed by search engineers.
Marketing to Webmasters
If your forum signature at Digital Point (sorry to stereotype, but it's just so true) contains links to three directories you own, you're probably in possession of three obviously manipulative directories. I'm sure there's a couple exceptions, but if I were Matt Cutts, I'd just tell one of my quality control guys to go spend a few days trawling DP for directory domains.
