I found it to be exactly the opposite -- I just let it sit there in my system tray and when I'm ready to check my mail, I click on it, mark messages for blacklisting/deletion and then process the mail. My e-mail client pops up and I'm all set to go.
BTW, Mailwasher uses the SPAMCOP database for it's blacklists. It still misses plenty -- really not it's fault since it checks by domain. Many SPAMMERS use fake domians or domains they know will be allowed through by these types of databases (AOL, MSN, Yahoo.....). So you'll basically be paying for something that you could have for free and only using one of the available databases while Mailwasher is using 3 (SPAMCOP, VISI & ORDB).
Each to his/her own I guess
-Craig