But what is the answer to SPAM?
I add a third vote to the comment that spam is the #1 problem with email and if Google is sincere about offering GOOD email services, then they would STOP delivering so much of the garbage. Even with a false positive rate of 1%, you feel you have to check it. Last month I think I had two of them, including one message that was moderately important.
However, I also agree with the other comment that Google has stopped listening to their users, though he left out the 'gone evil' part of it. I'm still wondering what I said to offend 'the Google'.
If Google was actually listening to scum-like-us, then I'd suggest they use this new feature to help fight the spam problem. Obvious approach would be to use the priority sorting feature to make sure that probable-spam gets put in a special really low priority queue, where some of the settings would prevent it from ever being delivered. For example, the default option could be for their system to automatically gather up the undelivered-but-probable-spam from many accounts, and once there were 10 matches, all of that spam would go straight to the bit bucket--do not pass go, do not screw with any company's reputation, do not support the spammers in any way, and do NOT bother me with this tripe.
Actually, I might prefer one-step above that for a human in the loop... For the sake of safety, I'd like the system to collect candidate spam and then wait for human confirmations by volunteers. Let me explain this version with an example: Imagine that Google has queued up 1,000 probable spams of the same category, with a very high similarity metric. The 1,000 recipients would have an option to confirm deletion of that category, and as soon as some small number of them, let's say 5 people, confirmed that it was spam, then all 1,000 pieces of spam would be evaporated and the the other 995 people would be saved the hassle. (Perhaps more importantly, if there was one sucker in there who might have been fooled into sending the spammer money, this could help prevent it from happening.)
My conclusion? Spam is NOT a law of nature like gravity or evolution. We humans defined the rules of the game that the spammers are playing--and we can fix the game to make spamming a much smaller problem. I don't think we can cure the kind of sociopath who sends spam, but I think we can encourage him to crawl under a different rock, hopefully a much less noticeable one.