A lot of people want throw-away email addresses for those sites that insist you sign-up before they let you have/see something.
I have a hotmail account for news-group posting with spam and filter rules set up so it rejects anything sent to it. In news groups, you should be posting/replying to the group, not to individuals anyway. Since you can't readily hide the headers in a NG post, this approach keeps the spam away.
Used to have a special account on one of my domains - e.g. blackhole@mydomain.com - set up so it didn't accept mail, but found I was taking a lot of traffic against it. Now MSN eats the traffic.