If you want to clear recent documents in ubuntu here is how you can. Just click on Places on the top panel menu, and select Recent Documents \ Clear Recent Documents and click on the Clearbutton when prompted.
The list of recently access documents will be deleted (not the documents themselves). But now you want to disable the view completely.
To disable, open up a Terminal window by clicking on Applications \ Accessories \ Terminal from the top panel menu and enter the following set of commands:
manohar@manohar-desktop:~$ rm ~/.recently-used.xbel
This removes the file recently-used.xbel (located in the root of your Home directory by using the rm command (this file is used to store the list of documents) Then give the next command :
manohar@manohar-desktop:~$ touch ~/.recently-used.xbel
This recreates the file with touch command. Then give the next command :
manohar@manohar-desktop:~$ sudo chattr +i ~/.recently-used.xbel
This changes the attribute of the file to make it inaccessible using the command chattr +i.
Next, clear the Recent Documents list as described above.
Now when you check Places | Recent Documents again, it should now be greyed out and disabled.
If you want to enable the Recent documents again, give the following command :
manohar@manohar-desktop:~$ sudo chattr -i ~/.recently-used.xbel