We have a customer who is very keen on putting as many links as possible onto his site. This was fine in the bad old days as even the mighty Google loved incoming links (which of course had to be reciprocated with outgoing links) but this is absolutely no longer the case. This particular customer decided to add himself to a link farm and then added said link farm to his links page using our Control Panel - then he wondered why he slipped down Google very quickly.
I have said it before and I'll say it again : link farms are a monumentally bad idea and you should avoid them at all costs.
If a site with relevant content links to you then by all means link back but think very carefully about the context of the links.
In fact, from now on we might just ask customers to sign a disclaimer or ban them from being entered into the Control Panel - they are that bad.