It looks like the number of passwords that I have to remember grows linearly over time. Since I don't have the best mnemotechnic abilities I decided today that it is OK to just forget them. Then, I just tell the whatever-site-I-must-log-on that I've forgot my password and ask it to send it by email (or reset it) each time my cookie expires. Then I simply cut & paste the password from the received email and voila, everything seems to work fine. This also allows me to implement real cryptic passwords without any fear that I might forget them later.

P.S. Yes, I know that SMTP is not really a secure protocol... :-)