Link Exchange may have branched off From SEO

But, now a there is relatively new branch of Link Exchange being called
"triangular" or "3rd Party" or "Three-Way"
under the theory that some SEs give an extra point of two to non-reciprocal Direct Exchanges

A sub-branch of this - is putting up a large directory with a Separate Domain name and directing all potential partners from various Web sites to post there. Under the theory that one larger directory where catagories link to each other will development a more Yahoo/DMOZ-like credibility, Increased PageRank, and SERPs as it grows larger and larger.

Search engines are wise to this strategy. Triangular linking doesn't work. Nor does creating large volume bulk links through article marketing. Pursue authority links from popular blogs and magazines (usually by writing for them).