Are we too smart to work 8 hours a day?

The question obviously comes from insight in productivity and actual efforts we make nowadays. To narrow the story down i would focus on project/solutioning based jobs and also because that is what i know and understand. I can say that active work on solution tasks definitely does not take me8 hours a day every day because it significantly varies. This is the fact of the job. Also, solutions are not only deliverables. It takes a lot of brainstorming, creative thinking and lot of time spent communicating with the team. Then when all is set and everybody in the project team are at least close to being happy, normally you have only couple of days to put everything together and make it accurate and presentable. So, measuring time doesn't make much sense i would say, but on the other hand that is the proof of our existence - proof of full utilization must exist. To override this problem, there are two options - one to do things much faster than expected which can be exhausting but beneficial, or two, to simply report in your working sheet every phone call or discussion you had during the day no matter how important it turns out to be. The reason i posted a question as i did, is because i do believe that we evolved from 'time sheets' times, but what is our preference? Now, it is obvious we can use various words, correspondences, meetings etc to prove we did some work - technology allows us to, but it is a time when changes are so rapid and we really have to think. We have to have imagination and creativity to adjust and predict, so utilization or hours spent in the office or whatever time sheet says don't mean anything anymore. Still many people, are wasting their valuable creativity in finding patches to fulfill the spreadsheet. Where is your creativity and how do you manage to 'work'8 hours a day?