The default filter can be changed without custom programming, but that change will be lost if the database is updated.

First, find the name of the filter you want to apply. In this case you only want to see "open" leads.

Second, activate developer mode. https://accounts.openerp.com/forum/Help-1/question/83

Third, edit the action for the view you are in.

Fourth, in the action area you will see Filters, and under filter you will see Context Value. The text in this box must have the proper grammar to work right so you must be precise.

The grammar is { "value_1":1 , "value_2":1 } if you delete the curly braces or forget a colon or comma between values, you will get an error.

Before the closing curly brace but after the last value put in , "search_default_open":1

Your context value box will looks something like - { "value_1":1 , "value_2":1, "search_default_open":1} now.

Save you changes, go to a different screen and then go back the sales > leads and you will now see the default filter applied.