I think Kmail really miss an easy way to manage spam by default. Thunderbird and Evolution manage it automatically without any tedious filter configuration. More than managing spam with bogofilter and spamassassin, mail marked as spam are automatically moved to each spam/junk online account folder. Same when you mark a mail as ham/not spam, mail is automatically moving from the junk folder back to the each account inbox folder. Kmail can only set one folder to move spam to from the Anti-Spam Wizard and when marking a mail as ham, it let the mail on the junk folder and do nothing with it. It miss some automatic things and as soon as you have more than one account it is really difficult to use.