The service i use distributes to about 1,200 places. This gives you a good diversity of links from different IP addresses which is also a factor the search engines consider with ranking.
Too many links from one IP address lowers the value of the links also. The more diversity the better.
I even make sure the directories that publish my articles get bookmarks to the page to build
pr to that page on the directory. This will make sure that the article is not taken from the directory.
Article directories remove articles in 6 to 18 months to save space, but if your article has a pr1 or 2, they will not remove it. Would you remove a page with
PR??
Once your articles are published, digg them and ask a few friends to digg them also, you can use any social bookmarking service to this. Most articles can build
pr to the page with just a half dozen bookmark links. And then you have a quality link that will stay forever with
pr.
I know, some do not want to build links to article directories, but this helps you and the directory. so it is a win/win situation for everyone.
Just another trick that helps a lot.