When running 'gem server' flickr-1.0.2 gem did not have any docs available (on OS X10.5 at least). So to add the flickr rdoc into the gem server :
find the location of your gems, you can use locate.
$cp /Library/Ruby/Gems/1.8/gems/flickr-1.0.2/doc/* /Library/Ruby/Gems/1.8/doc/flickr-1.0.2/rdoc
Now start the gem server and the rdoc link should be active.