Been there ,done that! Such crude dimming is probably ok for live music stuff, but for stage shows slow fades look real bad! The eye can generally distinguish a change of firing time of about 15uS - so if you want smooooooth fades - you gotta do equal or better than this.

Also, Gabriel mentions that his firing pulse was too short for the moc3021's. For loads apart from incandescent, you really need to hard fire the triac - keep the drive to the opto for the whole time you want it on - note the the opto/triac combo needs a little time to turn off before zero cross - 500uS -1mS. Read the specs for the opto and triac CAREFULLY! There is quite a spread in the parameters and what may work on the bench may fail in the field. There is some temperature sensitivity here. And don't forget your snubber across the triac - this protects the opto from voltage spikes that kill it apart from limiting Dv/Dt for the triac. Always use a choke to limit RF interference the bigger the better - it can also save the triac from overloads - if you're going to dim parlamps 16A triacs won't last too long when one of these lamps fail - go for the 40A ones if possible. For the most robust dimmer - use scr's - these are more likely to survive an overload with a circuit breaker. Triacs will almost always die before a circuit breaker trips.

Also it's always good to track the mains frequency if the system is run off generators or there is mains signalling in your area as this will cause disco effects when you don't want them. This can always be done in analog before it gets to the cpu.

So for a simple dimmer, shortcuts can be taken but for a professional quality dimmer methinks a faster cpu is in order.