Clean Tweets does various actions when you use Twitter Search at either Search.twitter.com or when you access search from within your web based profile.
It automatically deletes any tweets from accounts that are less than 24hrs old (or how long you specify). A lot of search spam comes from churn and burn accounts that spam until they get flagged so doing this cuts down on a lot of spam. (don't worry legit newcomers you can show up tomorrow).
Anyone tweet that mentions 3 or more (or what you decide) trending topics in it will not show up. Most spammers also list every trending topic they can find after their little spammy speal so this is a good way to cut down automatically as well.
Manual Delete Option. For the spammers that sqeak by or just list one trend at a time you can click an X by their avatar and it will delete their tweet and remove them from ever showing up again. (don't worry if you accidently delete your friend you can get them back in your settings)
It is pretty simple but in the days we have been testing it, it is very effective and cuts down on a lot of spam. The best part is it doesn't slow search, or change anything, it is like the spam was never there.
It provides a safer, more enjoyable Twitter Search experiance