While Twitter allows people to delete Tweets, often times those zombie Tweets were still indexed in Twitter's search. Apparently, that's no longer a problem.
MG Siegler over at TechCrunch has been doing some testing and finding that deleted Tweets aren't showing up in Twitter search. They're not even showing up in the search API, according to Siegler.
I did a small test myself and sure enough, my deleted Tweet was immediately removed from Twitter's search results.
So, now you can stick your foot in your mouth with a little more ease.