Things Blogger Should Invent: first-time only word verification

Blogger should have an option where users with blogger accounts are asked for word verification only the first time they post a comment on any given blog. Then Blogger takes that word verification to mean "Yes, this is a real person," and that user doesn't have to verify any more. That would still deter the spammers, because I doubt they want to go through in person and verify at each blog, but it would make things easier for regular commenters.