I've personally gotten traffic from some of those other bookmark and social network sites. I believe Ed's main intent was twofold.
1. To enable us to get up to speed with actually bookmarking and learning the process as quickly as possible. Face it; it takes time to create 28, or more, bookmarking accounts.
2. To suggest a wise course of posting to only a handful of sites at a time. 4-5, not 24-25 which could be seen as spammy. By all means, mix them up and see where your audience comes from after a few bookmarks. In my case, some people at Folk'd liked one of my sites, so now they are a permanent part of my socialmarker list for that site.
Liz
Twitter / Elizam