Do you think it is safe to use cookies in PHP?
Please tell your personal experience and what
will you advise to improve security.

Yes, I do believe it is safe. If you really want to be safe you could always encrypt the info stored inside the cookie with an md5() command.

Thanks

FYI, when i store passwords in a cookie (for Remember me option), i double encrypt the passwords.

When users register a secret string is generated and is stored in DB. Users' password is double encrypted like

sha1($password,sha1($secretStr));

ANd this is the password i store in cookie. Even though people decrypt this password, they wont get the orginal password.

If you want to be really secure, you can use the $_SESSION to store values on server side, while still making them available as long as that user is browsing your site. No files are sent, so there is no way for an end user to modify them.