.com or .net are preferred But you might find others that do the job But good names are in short supply in many instances for .com so other options need to be considered But here is an example of a really top grade web directory .org real quality eWebPages.org http://www.forplex.com/detail/link-434.html If you could create a .org anywhere near to that standard of quality, you will have done an excellent job
There used to be a benefit in terms of SEO, just using that TLD. But it's not like that any more. Matt Cutts said even blogspot link is as same as any other extensions. If it's true, the only reason .edu can be valuable is because of the fact that most of those sites are authoritive in education niche with high PR.
I don't think it matters. But for free dir, .org is what I think good is. For paid, .com and .net. This is just my guess, I may be wrong.
I think --it is the PR value of the page that matters. But I like .info as directories provide resources or informations
doesn't matter to me .. if i want to submit idc whether its a .in, .nl or w.e extension ... as long as its a strong pr and good backlinks ... i will get a link
Hope you got everyone's point. It really doesn't matter which extension you choose. Your success will depend on how much effort and time you put into your directory; such as content, marketing and link building.