netmeg - 2:15 pm on Aug 5, 2010 (gmt 0)
Obviously, the question to ask yourself is whether this directory will enhance your users' experience on your site. At least, that's what I tell my clients when evaluating link requests.
But the other thing you have to ask yourself too; if you spend some amount of time and money getting traffic *to* your site, do you really want to then send it off?
There are valid reasons to do that (and, in fact, my site with the most traffic does just that) but it's not for everyone, and it at least deserves thinking about.
For one client, his directory was very useful, but really not targeted to the same people as his site. So we broke it off onto another domain.