I agree... example I started a directory just on the basis of link exchanges
Webmaster-Link-Exchange.com in the begining I was using a manual link trading systems. I then found a good auto link exchange script that I could use to verify backlinks and disable people where not trading with me anymore. I did a manual audit while I was switching to new system out of 150+ links 40% of the links I could not find anymore. That is such a big head ache. But now for this directory I can run a report monthly and if my link is no longer on thier site I remove thiers very easily.