I usually have more than enough energy to spare. Of course, I work from home at a job that keeps me sitting on my rump for large chunks of time throughout the day -- but I also have two busy children, a puppy, and a fairly active life outside of my working hours. To hear my friends tell it, they are tired all the time and I probably ought to be as well.
The only time recently that I can remember being completely exhausted is when I attended the birth of my friend's baby in January. I was at the hospital with her at 6pm on a Friday night, stayed up for her son's arrival, accompanied him to the nursery and then stayed to care for him all night, until she was allowed to have him back around 7 or 8am (she had to have some pretty rough treatments due to her pre-eclampsia). Then I stayed with her the following day and night - I think I went about 48 hours or maybe more running on a couple cups of coffee and little else.
That's the first time in my life that I ever thought I might need an energy supplement. Of course, I didn't have time to google to find the best energy supplements, so when another friend of ours offered me something that she had with her that Friday night, I declined. I think I'd try to be better prepared if I ever had to attend another birth and act as the "baby minder" for hours and hours afterward!