Jonathan - 7:22 pm on Aug 5, 2010 (gmt 0)
Depends on a lot of variables.
Which offers more value to your visitors: an article on a specific topic, or a directory page listing 10 or 20 articles/websites/discussions on that same topic? Depends on your niche, and on the quality and originality of articles you intend to write. Also, can you crank out 10 or 20 directory listings in the same time it takes to write an article?
Can you allow user ratings and submissions without significantly sacrificing quality? Probably not, but maybe, depending on your user base. You will still need to vet every submission, but you might be able to recruit some DMOZ-style "editors" to review links for free.
You can easily check for bad links with a script, but, yes, you will occasionally have to manually and personally review every listing.
Per my experience and niche, directory pages do quite well with Adsense. You can also easily add monetized search with a Google CSE. Users will, by nature, be using these directory pages to leave your site. However, in your directory, you can include links to relevant content on your own website. Also, if your directory pages are genuinely useful, you will likely develop authentic inbound links to your site. A good directory page will out-meta all of its listings.
Consider your own current desire for information and perspective on potentially starting a directory. What would be the most useful resource for you right now? An article? A forum discussion? A wiki page? A Google search for "starting your own directory"? What if you stumbled upon a credible SEO directory, with a category called "Starting Your Own Directory", which listed a couple dozen human-reviewed, high-quality relevant resources?