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Once you're on those lists, you're on for the duration it seems.
This, fortunately, isn't my experience. I replaced most of the simple email addresses on my main site with javascript functions sometime in the middle of September, and, by the middle of October, most spam to these had ceased. There's only a couple of old favourites that keep trying.
I know that the harvesters are still reading my HTML and the spammers are still sending stuff, since one address hasn't been changed (for reasons that are irrelevant to this discussion) and it still gets spammed good and hard.
Seems like the lists are changed fairly rapidly, and if you find a way of becoming invisible to the harvesters you'll reduce the amount of spam you get almost overnight.