Please excuse me for crashing in uninvited with a bucket full of science.
1. Group delay is the same thing as phase response.
See: http://en.wikipedia.org/wiki/Group_dela ... hase_delay
group delay is the normalised derivative of the phase response.
2. Describing group delay as "distortion" is profoundly and deeply misleading.
I figured we had roughly all agreed that "distortion" (without a more specific qualifier) refers to "Harmonic Distortion"; the generation of harmonic content from the signal. Group delay generates nothing that wasn't already in the signal; it just offsets phases of different frequencies, in PRECISELY the same way that the EQ curve modifies the relative levels of different frequencies.
In any case, phase response (which is what we're discussing) is an inherent property of any linear system. A linear system (by definition) is one that does not generate distortion.
As a rule, usage of the phrase "phase distortion" is overcomplicating something very straightforward. "Phase response" describes the same thing without being misleading. Sorry for getting into semantics.
Unless we're talking about modulated reverbs, these are ALL examples of linear systems - they can't generate harmonics. They don't distort. EQs tend to have extremely short/simple impulse responses, Delays tend to have extremely sparse impulse responses, Reverbs tend to have longer and more complicated impulse responses. The name we give to an effect correlates precisely with what we hear it doing to the signal. Hence the grey area between "delay" and "reverb" that one might call "echo". Again, semantics.
4. "Fact 1: When you boost or cut frequency bands, it will boost or cut something unwanted or unexpected."
The truth of this "fact" depends on your experience, your signal, and your expectation.
When I boost or cut a frequency band, I have a pretty good idea what it will do.
I tend to use cuts for something unwanted and boosts for things I like. See how I twisted that? Again, semantics.
5. "Fact 2: EQ can indeed bring distortion, due to an effect called "Group Delay"."
As above. Not distortion in the sense that you would usually understand it. Nothing is being added to the signal; it's just being phase-realigned. This is a natural and expected consequence of EQ in both analogue and digital domains.
6. Prescriptive strategies for EQ are unhelpful in general.
When cooking a meal, how much salt should you add?
Hopefully, you'll agree that it depends on what you're cooking, and whether or not you find that salt improves the flavour. EQ is the same story.
7. Group delay can be implemented analogue, using all-pass filters.
It's a bit wobbly, but works fine! My favourite example was the old Focusrite Blue mastering limiter - completely analogue, but with a 10ms lookahead delay implemented with a network of allpass filters. Ace.
8. Delays and reverbs USE group delay in order to provide.... delay.
Hopefully you can see a link here. The clue is in the name. If, every time you read "group delay", you skip "group" and just read "delay", you're close to a decent working understanding of the phenomenon.
I've seen 2-4 samples (at 44100 = ~50microseconds) of delay from analogue EQs. That's about what you expect from a 5band set up to do stuff. 50us isn't much though. Reverbs use filters to achieve MUCH more delay. Typically at the cost of being able to EQ too much. Hence using all-pass - they're flat in magnitude response but give you the phase response (group delay) you want.
Enough rambles. Hope this helps.
Edit: Dammit. Just realised that article I was responding to was an advert. Sorry. I keep doing this. Anyway, hope the above is helpful. I'll be where I usually am if anyone needs me.