I have a couple of throwaway free email accounts that I use on these occasions. If it looks like I don't have to reply to an email from the site, I just make up a fake address - something obvious like noneof@yourbusiness.com or goto@hell.com.

Yep, sometimes it's too annoying, especially when you want to leave comment to a blog. Even my browsers cannot retrieve username and password when I need them. There are some tricks, but I want get information, food for my brain, and not playing desperate games with con artists and pranksters. Good I got reliable filters and don't remember when I saw spam last time. I hope it can be something similar against such cheap tactics on the web sites.