I have become a great fan of Digg.com but unfortunatly the new stories are swamped by spam. There is someone who is using a script to post spam stories at a rate of over 1 a min. Whilst you can ignore comments by user you cant do the same for stories. After a bit of lateral thinking I remembered Grease Monkey and sure enough there is a script to do just this. So one pain free install later and all the spam is gone.
I have had a browse around for any other usefull scripts but nothing else has caught my eye.