I was wondering the same thing, myself. I haven't really been tracking it, though. What I did notice is that there was a huge difference in efficiency when I went from level 6 to level 7 in my main weapon, and I only noticed it after completing 7 (so, the % in between didn't jump out and scream "I'm working on it")

I'm thinking that the interim percentages may have a part to ply, but it's the big numbers that really matter.

Of course, I just spent 7 skill points to get a 1 point increase in a skill with an 87% chance of success...so I hope those numbers matter.