If you are using Thunderbird (TB) on Mac OSX, you might be annoyed by that when TB opens an attachment (like a pdf file) it creates the file on the Desktop and then leaves just it there! I have finally found a solution, which seems to work at least for me and assuming that you also have Firefox. The solution is here, but I duplicate it here to make sure the idea spreads:
Simply open Firefox, in the address bar type in about:config, then add a boolean variable browser.helperApps.deleteTempFileOnExit and set its value to true.
Now, this works to the extent that when you exit Firefox(!!) (after quitting Thunderbird), it will remove the cluttering files.