I'd definitely make use of this feature. Some ancillary features might include: a) Google could warn you if it thinks the sites you have blacklisted seemed to

I'd definitely make use of this feature. Some ancillary features might include: a) Google could warn you if it thinks the sites you have blacklisted seemed to have regained credibility. b) Google could suggest additional sites you may wish to blacklist, based on other user blacklists. c) Google could allow outside parties to curate blacklists. d) Google could list the most commonly black-listed sites publicly. For the webmasters that find themselves listed who want to run an actual honest business, this is a good sign they should change their tactics. For the folks that aim to spam and profit... well screw those guys.