It all depends on how you reciprocate the link. If the sites are both relevant to each other and they are both quality sites it will help you. If you use software to automatically send out a billion emails to other site owners asking for a link exchange you may be punished or never even rank.
The goal is to provide useful content to the reader. Forget link building, focus your efforts on #RCS. If you get to a site that you want to link to, or want a link from because it will help your users, you are on a good path.
If you get to a site that has nothing to do with yours and you are able to get a link (reciprocating or not), be sure that it can help their/your users. Building links just to manipulate the search engine might get some ranking but not for the long hall.
Put yourself in Googles shoes, what would you want your searchers to find? A site that is recommended by all niche related sites or a site that is recommended by non-niche related sites?
