I really like that kind of puzzle games. Simple rules, deterministic outcomes and "that can't be done, because..???"-levels. I played a version from before 08/14 ( I suggest adding some version information into your builds, so you can see which version someone talks about). I'll be trying the new 8 levels soon.
The game is fine as is, some suggestions for things that would IMO improve some parts:
1) Some global best values for each level, so players can see if it can be done with fewer moves and/or fewer machine parts. Of course I understand that for that you need the ability to upload data from the game to some server, where you have to check the solutions,a.s.o which goes beyond a "simple" single-player game. Just some food for thought.
2) Planning routes in later levels, when you need to branch a lot, can be a problem because everything needs to be crammed into a small physical place. In earlier levels you can easily see where each packet goes because paths are seperated, which is no longer true later. I can think of two options:
a) When using the normal pusher tiles, if you move around with the mouse button pressed, let the previous pusher tiles change direction to follow where you go: From first pusher to second pusher, for example.
b) Give some clue where the paths are, like I try to do in this picture.
3) I like the iconography, but I can never remember which symbol is the stopper and which one the sensor. No idea what to do, though.
Again, this is a good game IMO!