I use a Das Keybaord. I've read the claims that you will be able to type faster with it, but I haven't seen an improvement here. I've tested my speed and it is about the same as what I can get on my laptop.
The boon for me has been that my hands don't get tired and sore. I was using a standard-issue Dell flat-key keyboard and every single night, my hands burned and I felt like my pinkies were going to fall of. My job requires near-constant typing, so this was a major issue for me.
The main productivity for me has been learning and getting comfortable with hot-keys as well as using the Vimium plug-in.
