Nope, looks good. I did the same with a similair moc and triac. Worked out great. Link to it in sig.
One thing to check is how much current/ how many watts that a light bulb etc uses and how much the triac can handle.
That is interesting.
The schematic look good, like sribow2 said, depending of the values of the parts ( currents , watts, voltage ).
I check this two site how a dimmer work.
The way I understand it, the input signal from the first opto-coupler going to the Ardiuno and an output signal from the Ardiuno going to the triac opto-coupler by "sync" with the AC voltage - chop it at the right time - to produce a dimming effect, using an PWM from the Ardiuno. The control is done in coding.
Now, I understand what you are trying to do. Dimming using software. Interesting.