One or two lines of HTML code at the top of your page
will tell them they are not welcome, if you don't want
them clogging up your site.
They are supposed to check every link and see that
they are correct, in fact if you have a lot of dead
links they are supposed to dump the page and don't
include it in their listing.
In some cases they can be good as your info turns up
in their Engine when searched, thats how you get listed.
You can have the opposite effect if you don't follow
common rules when designing your pages.
I just hope they start removing/replacing links from
the old forum, as they show up as dead since the
new format shifted to here. Can't be good for surfers
if they think every second Picaxe link will be dead.
PS: Just a quick search on Google and it
seems the links to the old Forum have gone. With
some 8,000+ Threads they will have their work cut out
for them setting up the new links.