Haven't had that problem before, far more of a problem when I try to register with site specific email addresses like d+hn@nblows.com which I've tried to get in the habit of doing.
Some mail providers (eg Gmail) use the plus sign as a label. So your everything still gets routed to d@nblows.com but tagged "hn" or "twitter" or whatever.
It's quite a convenient way to have site specific addresses while still only having a single mailbox to manage.
