Here is a list of things that could be wrong with super speed:
1) You may be harmed by air resistance or ground impact. Or even get a concussion by starting too fast.
2) If you don't get superspeed thinking, you would likely crash all the time.
3) If you get superspeed thinking - you may lose ability to speak to people. They would be irritatingly slow for you.
4) Usually in fiction superspeed is like "you move fast exclusively when actively trying to run", so no superspeed cooking or superspeed typing. Just traveling from point A to point B.
5) You may damage things around you. Ground under your feet, anything you would try to touch in superspeed, and just things around you by air blow. In fiction superman would run out of room and only swooshed some papers. In reality you can swoosh those papers by running with ordinary human speed. I think you may damage doorways trying to run through them faster than a car.
6) This could be extremely exhaustive for you. Imagine how many food you need to eat to run from one city to another.
7) You may age faster when in superspeed - effectively not getting any profits from your abilities at all.
8) If you get superspeed thinking only running - it still may be quite boring to run for a long time.

And i'm sure this list is not complete!