I hate when people say something like, "My weakness is that I strive to get an A in everything." Why do I hate it so much? Because this question isn't about identifying your weakness so much as it is identifying how you rectify a problem. If your weakness is something like I said above, then you fix the problem by trying not to get an A? Just do enough to get by?
What about, "My weakness is that I am a perfectionist." So to fix it, what are you going to do? Not pay attention to details or leave out certain things?
Instead, I answer it truthfully. I did use the time management answer in one of my interviews. I stated that I had a problem with time management all throughout college, but I have recently begun to fix the problem. I then identified my weakness in my app through my GPA my freshman and sophomore year, followed by the sharp increase in the more difficult classes. I also highlighted my decent MCAT score saying that I had to study hard and keep to a schedule to balance having a relationship with my fiancee, work and the MCAT. I finish it off by saying that I still haven't perfected time management, but those points should be noted to show that I have been working to fix the problem.
I think that makes the answer the most complete and shows that the problem is being fixed.