My brother probably has 5, or more, email accounts. That way if he's looking for something or making an inquiry, he'll use a certain account. If he's emailing family/friends he only uses his personal account. That way he knows which accounts to delete messages even before reading them, etc.
Lot of trouble to me (I can see having two) but it seems to work well for him.
But he doesn't do any forums/message boards so he doesn't have to do logging in and out.
Still don't see why, in the canuck's case and others, they can't ban the IP address. That way you can't get back on even if you change email addresses.