I'm not too worried about auto complete and the browser remembering the password since I am the only one who uses this PC and if it gets stolen then my e-mail passwords are the least of my worries. (For credit card sites I do tell it to forget passwords)

Refering to the original post - its bad practice to store activation e-mails or other e-mails with passwords. Better to write them down than store them in your e-mail.