[willfully_lost]

Look at the note at the top of the page you linked, Version 3 of the Maps API doesn't require a key.

[mildweed]

Not only does v3 not require an API key, as of Sept 28 (a couple days before the rate limiting went into effect) sending a v2 API key to v3 will cause the request to fail:

http://groups.google.com/group/google-maps-js-api-v3-notify/...

Sounds like they're laying the ground work for v3 to use API keys again.