Lamp flickers if dimmed up to an extent
A few things to try- and take extreme care as the author suggests- no shortcuts.


short out the indicator LED in case the MOC is not getting enough drive. I don't think this us your problem, since your flicker varies with the dimming, but as he mentions it it's worth a try.
make sure your load is 'simple' like an incandescent lamp. Get it working first with that before trying CCFLs or LED lamps. If you're using an incandescent bulb, try doubling the wattage of the load and see if it improves.
The 1K series resistor is very high-- you could try reducing that to 1/2 or 1/4 and see if it improves. 


(I would have put the load on MT2 rather than MT1 to minimize the dv/dt at the opto coupler, but I doubt that's related)