On my sites I use meta refresh codes for 403/404 errors so if a page doesnt exisit it gets fowarded to my main page, the code being <meta http-equiv="REFRESH" content="0;url=http://www.myurl.com"> <!-- --> Code (markup): Is this ok for search engines?
from a user experience perspective I don´t think that´s the wise thing to do. Instead let the user know that the document/article etc. he's looking for no longer exists or resides at that place. offer the visitor other possibilities based on his search query or page requested...