Not bad for a first effort. Certainly better than my first one, which I was not brave enough to post.

That said, here's some feedback:

1) The grid is awfully heavy. You might tone it down a little. For example, set the blending mode of the grid layer to Multiply (when using black lines) or Overlay (for white lines). You might also use a gaussian blur on the grid (perhaps about 3px).

2) Try to post maps both with and without grids when putting them online, because some people may want to print them, while others may want to use them in a virtual tabletop program, where the grid can generally be turned on or off depending on what suits the players.

3) Pmumble's comment about adding shadows to the cliff is good advice.

4) The scale of the bedrolls is a bit odd. They're almost 5' by 10', which is pretty large. Maybe size those down a bit? It's okay if they don't take up two full squares.

5) The walls on the camp site adhere strictly to the edge of the grid. It'd be a bit more natural to overlap or fall short in a few places -- the grid is there for combat mechanics. Players need to be able to see where the grid is, but the features of the map -- walls, furniture, etc -- don't necessarily have to conform to it.

6) The resolution is a tad on the low side. Try designing at 100px to the square for most maps. It allows for nicer detail, and prints better.

I've done 50px-to-the-square maps myself, but generally only for really, REALLY big maps like Castle Venatris, which was 140 squares by 100 squares. I actually made that one at 100px to the square, but it was so big MapTool couldn't handle it. So I had to reduce the resolution.