directory in site:any problem for seo?

[frank1]

well,
we have a portal site which covers various areas and have many section.It is well taken by google and is ranking well for many keywords...giving us good trafiic...

now as a new section we want to add a web directory section where user can add their websites(approved...)...

so is there any problem in have directory in site?

will it effect current ranking negatively...in any way (can it?)

whats about outlinks ,bad neighbourhood....i fear out site is then taken as link farm and is discounted....

so should we really go along considering seo of the site...

if there is really potential pitfalls then we are planning of sub domains...

thanks