I have a few different e-mails and have had them for well over 5 years - they are all out on the net, in chat boards, on the newsgroups, etc.
I also own a few domain names and have a few other things out there that get the addresses about.
Also, awhile back I was signing up to gambling sites so that I could read their code to see if there were any security holes.
After all of that, I was getting about 500 spam a day (I have my accounts all setup to forward into one central account).
I changed a few settings and setup a series of filters - including SpamAssassin in there.
As a result, I'm down to about 100-150 a day now and they are nearly all caught by SA. Off the 15 or so that get through everyday (it would be better than that, but I lowered the aggressiveness of the spam filters for a good reason), probably 14 of those get caught by Mail.app on my laptop.
All in all, I don't pay too much attention to it.
I pay more attention at work where I have written code specifically to trap spam there - it is also key to make sure that the servers aren't being used as relays (easy enough, but it is harder if someone on the inside of the firewall authenticates into it).
I have a stats page up on my website that tracks how many messages and at what hours they come - I like stats.