I change my login grace time to 3 seconds, you either have the key or you don't :) No password entering

Nice idea until you're logging in from a slow/overloaded connection, or your ssh host is being flooded with traffic, or has a runaway process that's causing it to thrash, or lots of other reasons you might want to use ssh.

I can't think of a scenario where a really short login grace time would protect you from an attacker, either. What's the motivation?

Hmm, good point, with keys, 30 is a bit long these days.