I think you got lazy (like most of us lol) or made a mistake (like most of us lol) because I think you took the bottom half of the light bulb and placed it there (or something in that position) and it had a white background. You can lightly see the white box around the bottom of the lightbulb. I would have thought "hey it's a flat white background and going on a flat white background, makes sense that you won't see it" except that you put a slight gradient in the background and now the white box shows up just a bit
That, and critically, I don't like the 3 different fonts.
1"Next time ... note of it!"
2"Post-it..."
3"Useful for:..."
Granted, I think they're similar, but they all different tracking. Also, I think that the tag line should have been much larger, or at least larger than the Post-it motto.
Then again, you're already finished. I love the photoshop collage.