@Grumpy_mike: Feel free to poke holes in this design as well! Of course all designs are a trade off between price and performance. If you have a link to a design that does not require a current sense resistor then I'd love to see it as all designs that I've seen use them.
Don't be scared of all the connectors on the top. The real circuit is in the middle row, and consists of (left to right):
1 pot that lets you pick the current
1 resistor (R13) that just stops drawing too much from the opamp
1 connector (T1) Where you would pull down to turn off the circuit (i.e. PWM)
1 darlington to burn away the extra voltage
1 resistor (RSENSE1) that senses the current (you can use very low values, .1 to 1 ohm for example so heat dissipation is not such an issue with this resistor)
And on the far right SV1 is where you hook up the LED.
In short, the opamp uses feedback to equalize the voltage across RSENSE1 and the pot.
The PCB is essentially 4 of these, but certain parts (namely the opamp) are quad so its just one chip...