After upgrading from Toad 11.0 to 11.5, large scripts are slow to load when logged in as APPS schema. This is not a problem in previous versions of Toad and is not a problem when logged in as other schemas (just APPS).
Open file, and as it displays in the editor window, the script text displays quickly, but the editor seems to take longer to draw out the code folding lines in the editor. It is hard to navigate throught the script why it's still drawing (i.e. up/down arrow key, page up, page down, etc). The Navigator panel is slow to refresh sometimes, and trying to navigate by clicking on the procedure in the navigation panel does not jump to the procedure in the script.
Use another schema when trying to review large scripts in editor.
Go to View | Toad Options | Editor -- uncheck the "highlight stored procedure" option.
Waiting for fix in a future version of Toad for Oracle.