My team's training schedule is set up in minutes. One of the things that always bothered me (for long-term development) is when guys race each other every day in training. To get around that I went to minutes. I find that it helps us do our training more relaxed. For example, on our long days if I used to give a 15 mile route that I wanted relaxed pace (say 7:00 miles) inevitably a few guys would hammer it out and be back in 90-95 minutes instead of 105 minutes. Now I just say, "here's the route, today's workout is 105 minutes, if you're back early add on until you get to 105 minutes".
My own logbook, like lots of people here, I keep both. Makes it easier to compare to 10-15 years ago when I was more mileage focused.
My college coach had a good idea on how to record mileage...Under 10 round down, over 10 round up. I've seen some logbooks that are in the tenths of a mile-way too much info for me.