Listen I dont want to slate anybodies business, they spent time building it and its not a nice feeling to see it disappear. But if your going to build sites build them for your visitors not for serp`s.
Natural linking, if your purchasing links from other sites get "nofollow" tags.
PR pumping your site or your customers sites is endangered. Building directories build your content around the sites you allow into your directory.
Dont be greedy it pays in the long run.