Edges and corners are presently very easy to figure out and provide simple starting points. To increase difficulty, you could allow pipes to wrap off the edge of the screen and continue on the other side. This would eliminate the obvious starting points.

I would like to see the elapsed time while doing the puzzle. Thanks for this great game!

I was thinking how you could turn this into a multi player game... =D You could include the option of being able to play a particular board configuration by using a seed number - e.g., '56732' would always give the same initial pipe configuration...then players could all play the same board and compete to finish first! And I'm sure with a bit of thought I could come up with something cool using bluetooth too ;)