Personally, i interlink my sites for traffic aswell as backlinks. My sites get indexed every day, so my interlinking a new site, it gets spidered quick
I thought the first post in the thread was more about the fact that all the directories on DP sort of have each others links in them back-and-forth. Personally I don't think that kind of interlinking would ever be a problem. If all sites 100's are on the same class 'c' ip that might ring some alarm bells.
Maybe this is one of the reasons why big directories don't buy too many links from directories and make it harder for directories to buy listing from them.