Removing Recently used items in 12.04 [duplicate]
Possible Duplicate:
How do I delete the entire history (Recently Used Items) in the dash?
How do i remove items from my recently accessed file in ubuntu 12.04.
If you want to delete all the recently used items entries in a defined range (for instance: last hour, last day, etc), or just disable this feature you can use the Privacy
application (installed by default on 12.04).
If you only want to delete specific entries i recommend you to use Activity Journal
(available in Software Center). Just left click on the entry you want and choose "Delete".
Go into System Settings. Pick the privacy app. Set the time range you want to delete for, and delete.
While you're in there you might want to change things to avoid certain items ending up there in the first place.