Not only does v3 not require an API key, as of Sept 28 (a couple days before the...

mildweed on Oct 27, 2011 | parent | context | favorite | on: Google warns that rate limits, overage fees are co...

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.