In general, exchanging links aren't that popular anymore these days, because of several reasons:
- Lots of reasons have been mentioned above in this thread.
- Link exchange with the purpose of getting some share of the other site's page rank or search engine ranking could be done via other methods.
- You may get 20 quality links this way, but after some weeks or months, the webmasters of some of those sites gradually add more links to the same page, which may result in two unwanted situations: 1) due to lots of other links form that page, your share of that page's rank reduces; and, 2) when the number of links exceeds 100, the page is seen a spamming page by search engines like Google.
- Link exchange creates lots of worries as you're not sure about the performance of the other other site's webmaster or linking project manager.
- It gets you few quality links compared to lots of time that you spend for link building campaign of this type.