Responding only validates that there's a person behind the address; then your name & address are placed on the "Verified Addresses for sale!" lists.

I'm lucky in that I manage my own domain (www.infinethosting.com will give you one for about $10/month). I route all my "real" mail (i.e. corporate stuff and friends & family) through my real address there, and when I need to sign up for something on the web, I create an alias there that just goes to my account. For example, when I registered for the NWA E-mail promo bonuses (10k miles if you let 'em spam you, or something), I just created 'nwamail@<domain>.com'. Now that's just an alias for 'my_real_id@<domain>.com' but I have filters that trap stuff sent to nwamail and throw it in a 'junk' folder. When I have some spare time, I browse the subject headers in that folder, and typically just delete everything en masse.

It's not a perfect solution, but it's a lot better than getting interrupted with the spam every day -- at least this way, once a month or so I can visually scan a couple hundred subjects, and delete them all in a couple minutes.