I've posted about this before (ages ago) and not gone through all the posts on site stuff to see if this is a recognised problem or if a fix is coming.....
But
Please, Please, stop returning threads that have expired in the results. If I search for something and the ideal thread comes up in results it s VERY annoying to find it's a chat thread from 1885 and so no longer viewable.
I also find the search pretty poor in general, returning things that are not really related to the search term. I find searching for a phrase or word in google followed by "mumsnet" returns links to relevant posts without having to wade through crap.