1 mailbox for mailing lists.
1 mailbox for mailing lists that are *cough* sensitive.
1 mailbox for everything else: general correspondance, website subscriptions, etc.
and I have 1 mailbox @gmail for attachments and friends to use, but I only check it when someone tells me to do so.
I used to have several different mailboxes for "everything else" - one for my domain (geekdrew.net) registration (admin@), one for general use (drew@), one for website registrations (public@), and others. I decided that I was getting a sufficiently low quantity of e-mail that I'd rather just see everything in one mailbox (since that's what I eventually had Thunderbird do anyway), and that the other accounts were just overkill. So I dropped the other accounts, and put forwarders on them, to my general account.
<edit>
Also, used the catchall method, creating unique addresses, such as atot@, for about a day. I then decided that it *really* wasn't worth the hassle, and would probably come back to haunt me, if I ever needed my password reset, and couldn't remember what e-mail address I had registered with.