Had a 2vs2 match PT Vs PT I used a probe to scan early and be in his base the first 6 minutes, no detectors at all. The only thing was an orbital command. I then used my allready set up warpgates to spawn 5 Dark Templars.. I know they had the orbital command so i kept 4 hidden and used 1 to attack his mineral line. He used the scan from his Orbital and so i used my other one to herass some more. Again a scan. and he just kept using it. it was used 5 times vs me and i just couldnt counter it because by the second wave of DT's the protoss enemy made his observer allready. So my question is: How to be effictive with cloaked units in general when an orbital command is used?
Hide your dark templars in a mix of other units. By the time they realize they are dealing with DT's too, they have done a load of damage.
The same applies with any cloaked/burrowed units. If you lucky your initial assault may have taken out any detectors, so your cloaked units and what's left your strike force can keep on wreaking havoc.
You could also wait to he calls down his mules, if people are a little slow, they might get some surplus energy and therefore have enough for some scans. But if you wait til he calls down all his mules, he doesnt have energy left over, and the dark templars will have a feast of SCV killing.