This would mainly only work against scrapers, tho, and not so much for account creation.
My argument is that Google could have done better to offer a completely different solution (e.g. some sort of proxy service) than to add a (apparently fallible) whitelist to recaptcha.
Another alternative that comes to mind (albeit much more complicated) is link encryption ala SpikeStrip: http://www.cs.ucsb.edu/~ravenben/publications/pdf/spikestrip...
This would mainly only work against scrapers, tho, and not so much for account creation.
My argument is that Google could have done better to offer a completely different solution (e.g. some sort of proxy service) than to add a (apparently fallible) whitelist to recaptcha.