Steve from Alledia has just written a blog post regarding hidden links in Joomla modules and components. He highlights the latest version of Joomap (a component we use here) and gives some sound reasoning for using the Joomla Credits module to link to the third party extensions in use on your Joomla Site, while removing the hidden links.

Most of the time the credits module may be inappropriate for the function of the site, particularly if the site is non web related, but it certainly sends some kudos to the developers without risking being penalised by google in association with the hidden link tactics.