The more and more you learn about a language, the slower you get IMHO. It takes longer to finish something because you now care about the "right" and "wrong" way to do it. You build in far more fail-safes, you adopt programming practises that you feel are the "right way", even though they take longer. You explore the creation of your own modules / libs to handle repetitive tasks, but then refine those over and over. You take more care with the layout of your code, the security of it, the structure of the file system, etc. It's at this stage that it takes the absolute longest to finish something, because you're just never quite happy with it, too busy comparing it to the latest book / blog methodology to be released.

Then you hit a point where you realise that too much messing around,too much worrying about the minutiae, actually leads to a far more drawn out process than when you were fresh and new to a language. So you settle on techniques you know work, perhaps refining them slowly as time allows, and build a framework / way of working that allows you to ramp-up that productivity level again. Do you ever reach the same level as at the start? I don't believe so. Your code is all the better for it, it gives you far less headaches going back into it than something written X years ago, but at a cost, a time cost.

I think this applies to not just programming. I've seen it happen with straight HTML people as well. Usually when they hit the "learning about proper CSS / accessibility", which initially slows down the time to build a site massively. But the more and more they do it, the faster they get until back at previous output levels again. But I would wager even then, not the same speed as before when quite frankly font tags rocked and tables and pixel spacers ruled the layout.

Perhaps this applies to graphics too? I don't know, because I don't consider myself a graphic artist ("photoshop dabbler" would be more accurate). But I could see how the more you are influenced by others designs, the more you strive to achieve that level of quality also.

These are of course only my thoughts, but that's the whole point of the commentary section of my blog.