Sometimes you may think you got a good link exchange when you really didn't. Some partners will try to outsmart you by sneaking in the "no follow" tag into their entire page or in your url. I just found this useful tool at http://www.seohosting.com/toolbox/no-follow-url that spots out pages with "no follow" urls.
Wow.... that's a lot of work to enter each URL every time... if you have Firefox, here's a great way How to Easily Spot NoFollow Links