It is also very buggy around fullscreen apps, enough so that I stopped using it after a week. Slate et al worked much better for me (still slower than TWMs on linux) but forced or at least tempted more setup which is definitely the benefit of Amethyst.
It is super buggy for fullscreen apps. Unfortunately, I have this superpower (or curse) of not being able to reproduce bugs. Every time I get near a coworker's computer, whatever they were talking to me about starts working.
There's a long thread on github about this (https://github.com/ianyh/Amethyst/issues/254). I'd love to know more about your set up. I've been trying for weeks to make it work for people, but Apple's APIs for this are kind of crap. And by crap I mean non-existent. I've started using private APIs to do things like figuring out whether or not the current desktop is a fullscreen app.
I came across that issue and might contribute info in the way of reproducing bugs, but my setup is pretty simple: near fresh Yosemite install, one Chrome window, one Finder window, and two Emacs.app frames (one fullscreen).
