Then it comes time to sign up for a new service and I never really know which email address to use.
Like when do you use a personal email addy, when do you use a school one, a work one?
Do you have a "spam" address? Do you ever use it?
1. Work
2. Friends, family, and signing up for free services that I want to identify myself with
3. Commercial transactions (anybody who has my credit card)
4. Anonymous address (which I use with websites that require signup but I feel have no business asking me). I personally use my real identity online for historical reasons, but if I didn't, I'd use this one.
[Edit: to answer your other question, they all get spam]
Edit: Really I would recommend you get your own domain (not a joke one) and use an email address there which you can carry around forever. You can always forward to gmail or whatever if you don't want to deal with spam filtering etc.
With filters, using the +blah functionality (email+spam@gmail.com for example), it works great! Never need anything else.