You nailed it right on the head - It's a lot more than just a PWM driver. The combination of a very smart control IC and an appropriately chosen FET, make for a really efficient LED driver. Not that I would, but theoretically, this driver design could drive 5 strings of 18 XPG's @ 1000 mA per string- in a parallel wiring scheme. That's a lot of LEDs for a driver that only costs around $25 to build. Of course my little board would probably melt down trying to drive a load like that, but with proper design and component choices, it is possible.
The UA7805 is a 5 volt regulator that is only included in this particular design to provide power for a Nueventics "Synjet" Led heat sink cooling system. The "Synjet" cooler only pulls about 80mA while in operation, so it's current demands will be very light on the 5 volt reg. In any case, The regulator has plenty of "thermal vias" under it to wick the heat generated by the regulator to the bottom plane of the PCB. The "Synjet" is another "smart" component in the lighting system, as it will respond to the same PWM signal as the LM3409, thus it will speed up or slow down it's operation speed based on the dimming signal from the Led driver dimming controller.
I'll be experimenting with this little driver over the weekend and I'll post my results. If I can get it to behave predictably, I'll post the info so people can create their own.