I think everyone is aware that we aren't going to be able to completely eradicate spam. As bots become more intelligent our defence against them must improve as

I think everyone is aware that we aren't going to be able to completely eradicate spam. As bots become more intelligent our defence against them must improve as well. I like that this is a non-intrusive technique that seems to have met with some success. It doesn't matter that the method is not perfect, nor that it is possible for bots to engineer their way past. Innovation in the bot detection space is the only way to keep up with the spammers. I would be more interested to find out if the method has any impact on accessibility, for example if screen readers are unable to use these forms. I would guess that anything designed to be visible to bots will also be visible to screen readers.