Is directory exchange links effective to increase PR?

[PowerUp]

Hi, I'd like to check if having a directory in a niche, and then exchanging links with other websites can increase PR.
Would google hurt me since I am linking to them and they also linking back to me?

[chinaeguide]

don't think so, google will not do that

[Marcia]

I have a very small niche directory that has a number of recips from several years ago (all related and on topic) and it hasn't hurt at all. But no recips are required, there are one-way outbounds, and it's a clean site - no links sold, nothing dodgy.