The term "human-powered" mainly refers to directories, i.e. online catalogs that categorize websites into thematic sections. Yahoo!, along with the regular Web search, offers one of the most complete catalogs on the Web.
When you submit a site to a directory, it is queued for editorial review. Usually, when you submit, you are allowed to choose the category your site will be placed under, as well as to enter the desired description and title for your site, which will show in the related category. However, the actual presence of your site is subject to the editor's decision when he or she browses your site.
Directories DO NOT accept automated submissions and have special means to protect themselves from auto-submission software. You should always submit manually to a directory.
What the directories are useless for:
With the directories, there's no such concept as "ranking", because once you've been included into the index, your site is ranked within the appropriate category by an independent factor, for instance, alphabetically or according to the Google Page Rank.
Thus, the concept of "optimization" has no bearing when applied to directories like DMOZ or Yahoo.
In terms of traffic, these directories are also of little value. The percentage of surfers who would prefer browsing categories in a directory over a regular search is quite small; few people tend to dive into the depth of the branchy vertical hierarchy of categories. Thus, your category listing won't bring you much traffic on its own.
What the directories are useful for:
Because the directories are compiled by humans and for humans (unlike the search engine listings which are compiled by robots for humans), the relevancy of directory results is very high. Search engines know that – almost any search engine spider starts its regular crawl at a directory like DMOZ or Yahoo. If you are listed there, the search engines will find you during their next crawl, even without your submission.
Additionally, directories themselves have high Page Rank values (as a rule). When you are listed in a directory, the directory is linking to your site. This link is considered high-quality and is very good for your overall link popularity, which is an influential factor when it comes to ranking. For the search engines that are able to analyze the context of your link (such as Google), your directory listing will be important because your link is supplemented by a relevant description.
To submit your pages to the Yahoo! Directory, it will cost you $299 for an annual review ($600 for adult-related sites). If you pay, you can possibly get listed within a few days. If you go the non-commercial route, it can take months and quite often they won't list you at all. The registration at the Yahoo! portal is still required for both cases.