Weird! I'm nearly the same - I can sit in front of my machine for most of the day, completely unproductive, and then in the late afternoon it's like there's a switch in my brain and suddenly I can work without any distractions at all. What really botheres me is that I finish nearly every day thinking "I'm just going to do exactly what I've been doing now, but first thing in the morning, and then have the afternoon and evening free", and it almost never happens. I just can't find the right focus/frame of mind until after lunch. It's extremely rare that it happens.