Argh, banlist....
I heard that 100+ bans are added every single day in DOTA banlist....
Man, when I was playing DotA heavily I probably added close to 100 a day myself.
Banlists are just a personal list of players you never want to play with again for whatever reason you deem worthy. It's a local list so it's not like this person is going to be banned by the world unless they're a moron. I don't see how a website is going to work at ALL. I'm not going to alt tab to search every person in the game before I launch.
Banlist for WC3 would search your personal banlist in real time, if a banned person came in it gives an audio cue "Banned player detected" and pastes to you clip board the reason they were banned. You can have it just auto kick that person out of the game.
Frogboy said something like this was going to happen in game where you have a personal banlist. I'd prefer a 3rd party program because of their versitility myself.