I using trade script for exchanging traffic,and link usualy look like this one: out.php=domain.com .Since it goes to out.php always it cannot be threated as hardlink.But there is also option to generate trade link as clean hardlink,which will generate <a href="http://domain.com">domain name</a>.If i pick that kind of url generation,will be good to put no follow tag on them?I ask beacuse some people say how putting nofollow tag on everything could effect your seo traffic. I noticed you can get traffic thanks to those hardlinks,for example let say you have site about sauseges and you put a hardlink to viena sauseges and then you receive traffic for viena sauseges keyword which is paradox since purpose of putting that hardlink was to benefit url where that keyword lead.So i think with putting nofollow tag on hardlink will be lost benefit of hardlink keyword but again could be compesated by repeating that word in rest of site.
I generally no follow those type of links, but I never thought about it. I just assumed by no following, I was keeping more of my PR juice for myself. Maybe that was wrong.
On your homepage (index page) - definitely nofollow. On other pages it really doesn't matter. Especially on blogs.
To summarize, do follow = both traffic and passing of PR juice no follow = only traffic and no PR juice (advocated by google for linking and not for link sales!)