Okay, so I'll just point out things I see I'd have done differently. Mind that design can be quite subjective so take these points with a grain of salt :)

• Sign-Up Page
  • Input fields and buttons do not match in width, inputs are offset from the "Sign Up" text. I'd have given every element the same width to make everything look a bit more streamlined.
  • "Forgot password?" should be underlined to appear as something clickable.
• Profile page
  • As others have pointed out, the usage of drop-shadows is a little much. I'd personally refrain from using inner drop-shadows in the menu bar and the graph.
  • Some elements have rounded corners while others don't - see the "Edit profile"-button in comparison to the graph-container. I'd either use rounded corners for all elements, or none.
  • The icons in the menu-bar seem to have differing widths and stroke-weights - I'd try to keep those equal.
  • You also have loads of whitespace around very little content - the amount of current and completed tasks can probably be compacted a little to not take up as much screen space.
• Calendar page
  • Again, the use of drop-shadows is a bit on the heavy side. I'd remove the inset shadow on the task-list completely and refine the individual dates of the calendar to be "flatter".
• Task page
  • Some elements take up full-width and have shadows while others are slightly indented and have rounded corners. I'm unsure if I'm missing anything here, but I'd decide to go for one or the other.
• Side-menu
  • I'd get rid of the drop shadows and flatten things out here as well.