I am a touch typist and almost never have to look at the keyboard. However, I could never use blanks because of the password requirements I work with - and number of passwords and PINs I'm forced to keep. Once we get into special characters, and numbers I get very inefficient with blanks (note: I use a 60%, so no dedicated num pad). Because I can't see what I'm typing, and I'm limited to very few bad attempts it is pretty important to make sure I can confirm the keys I'm hitting. I used engraved caps for a while, so they did look blank for the most part, but when I needed it I could look to get a visual cue. I don't think it would matter if it was top or side printed, as long as I could see it when needed.