This would be a block that when cycled with a certain number of input pulses, produces an output pulse. After which it resets the count cycle. Right clicking on it would show a screen where the user can set the counter to determine the number of input pulses needed before it produces an output pulse.
The idea is to use this to produce more complex redstone circuits without taking up huge spaces to achieve the same results. Useful for making more advanced clock circuits, or perhaps have a certain number of times a pressure plate can go off before triggering some event. It may also be great for making automated factories, if things like allocators go from being a mod to an actual implemented part of the game.
This item may not be that cheap though. I picture it using 4 redstone torches, 4 iron bars, and a block of stone.
I didn't think of it at first but I'm also liking the point made by David Bramblett. Give it a bump too...
It would probably be important to be able to reset the counter at will. To this end I would suggest that there be one input and one output on the counter, front and back that would govern the counting, while input from the sides would reset the counter to 0.
And if you're wondering "Why not just do it the old way?" I found a thread that gives an idea of how big such a circuit can be. Even when made "compact". viewtopic.php?f=1020&t=242332
Now imagine all that and the equivalent functionality fitting into one single block. If team MoJang can do it for something as simple as a repeater (and with multiple timings) then certainly something a bit more advanced could be compacted to take up a lot less space.