Yes, I have already tried it (and it’s secure). But, for example, If I host my blog in a shared web hosting, other users can see my wp-config.php (in some cases) and, then, see my password.
A password stored in a database is secure and however it isn’t stored in plain text. I think admins shouldn’t be able to see password of the users.
making a md5 (or another one method) of the password is one lawer more of security for a web site, I think. If ever someone hack my web hosting, I dont want he can read my password.
I now wp-config.php is very secure, but I think my reasons are reasonable. I don’t doubt about security in wordpress, of course, I really doubt about hosting and admins xD