Good point about having difficulty in finding the links.  I even had problems myself on checking things a few days ago.  
Originally I'd only set them up to show where the topic number is 4500 or higher.  Seems an odd way to do it I know, but the reason is based on fear of what search engines may do.  Basically there are theories that if search engines see too many of some particular links on a site, it may result in some search engines downgrading the ranking of a site in their search engine results pages.  Because of this and taking into consideration we've got just under 5000 threads here at BaO, I figured that if the links were added to just the threads numbers over 4500 it would hopefully be a small enough percentage of pages for the search engines not to inflict a penalty, plus would be OK for members as the links would show on the more recent threads.  
After doing this I've noticed that there are still a lot of live threads below number 4500 though, so I've used your suggestion about placing the links on the index page.  
 
By the way, I reaallly like Ask.com ... BaO is number 3 there for the term 
harry potter forum 