I have heard that mechanical keyboard improve typing speed. Is there any research to support this? I am considering getting a mechanical keyboard, but I already type pretty fast (90 wpm) so I am unsure if it will help.
The argument for a mechanical keyboard is that you don't have to press as hard and get more tactical feedback. Tactical feedback matters (my typing speed is lower on the iPad). I haven't tried a mechanical keyboard, but it stands to reason having to press slightly less distance can speed things up. Especially since you already have a fast typing speed.
I also think back to the old non electric typewriters where you had to push each key much harder. This made typing significantly slower because more force was needed. The new mechanical keyboards presumably wouldn't have this problem, but if you get a cheap one, I'd make sure.
Compared to what? If you are already 90wpm, then I doubt you are currently using a virtual/touch-screen keyboard.
Are you talking about a sharper click sound on your keyboard? Most people don't like the noise, but if you work alone it could be OK.
I like a curved "ergonomic" keyboard like the Microsoft Natural series. Someone asked about ergo keyboards here: Do ergonomic keyboards/mice provide significant productivity improvement over "average" counterparts?