Here are a few ideas: Mid/Side processing, separate Left and Right processing, pre and post curve analysis
But the biggest in the case of QuadCurve EQ is when I need more than one EQ on the track

Disclaimer: I'm not into a wine-tasting mentality with compressors, EQs, etc. I don't need an emulation of the legendary EQ from a legendary mixer that was used in some legendary studio to record a legendary piece of music; what I need is something that will cut and boost at frequencies of my choice in different ways 
 
That said, you might find this article interesting, as it describes how to use noise to evaluate the QuadCurve EQ (as well as other EQs). One of the QC's limitations is that it's not phase-linear, but SONAR has a phase-linear EQ so you're covered. For an interesting test, set up the Sonitus and LP-64 EQs to the same high-frequency boost settings, then switch between them on something like ride cymbals...you'll hear a difference.
 
For me, the main limitation of the QC is the number of bands. Four bands isn't really enough for mastering, although it's a toss-up whether you want to use the QC or the LP-64 for mastering anyway. I do like the Hybrid mode when there's program material with resonances that need to be but also needs gentle boosts; the "Pultec-like" Pure mode is great for general tone-shaping. So when I do use the QC for mastering, I usually feed into a bus so I can get two QCs in series and end up with 8 stages.
 
The other limitation is the spectrum analyzer. It's a welcome addition, but doesn't allow for averaging, hold, etc. 
 
But as a general-purpose, highly versatile EQ, the QC is tough to beat. I think some people who have a strong preference for a particular EQ might not be aware of the effect of the different QC curves, so they choose an EQ that defaults to a curve they like. Its's really important to become intimately familiar with how the QC curves affect sound so you can use the right curve for the right job.

Craig thanks, I read the week 59 article before. I understand that your answer is that eq curves is the principal reason why you would look into other eqs. I suppose the eq curve shapes is separate field of science available to most experienced ears only :-)

+1 for more bands. 8 total might be good enough, but not discounting the impact it might have on the UI controls. 
 
+1 for >1 instance in PC. Would be more than OK with just 2.
 
Might be useful to save "EQ only presets" instead of full PC presets. This could apply to other CW PC modules.

Hi,
A little bit off topic,but LP64 would be a great tool if it had a spectrum visualizer .

QuadCurve EQ Demystified
http://blog.cakewalk.com/quadcurve-eq-demystified/
 
But why is it mystified in the first place?
I have no time for this nonsense. Just name them by what they do.
 
Hybrid and Pure, OK, I guess I can easily see the difference.
 
But
 
E-type? Isn't that a car?
G-type? Isn't that a spot?

...and whilst we're about it, can someone once and for all explain what the Gloss button does? In normal, technically understandable terms?
 
I can't hear any difference.

jackson white
+1 for more bands. 8 total might be good enough, but not discounting the impact it might have on the UI controls. 

 
-1 for more bands. quad curve is like a channel strip EQ on a console, just consider ...

• how many analog consoles come with more bands per channel?
• not even new digital consoles come with more than that e.g. top seller X32 comes with LC plus 4 bands per channel (=Bark of Dog plus Quad Curve)
• more bands would be a nightmare to use with current screen estate and of course would no longer work with existing control surfaces (as their plugins are no longer maintained)
• when making some sound decisions already while recording (and not deferring everything to the mix phase), you can do a lot with 4 bands ... I know this is old school, but start to believe more and more in that ...
• there is special EQ for special purposes; a channel strip EQ can't fit every purpose (e.g. mastering, or really precise surgical corrections like notching out digital hum, ...); everyone of us owns at least 5 other EQ plugins and it pays to get to know them really well ....

 

jackson white
+1 for >1 instance in PC. Would be more than OK with just 2.
 
Might be useful to save "EQ only presets" instead of full PC presets. This could apply to other CW PC modules.

that indeed might be good ... although it can be done by dragging any VST EQ onto the pro channel ... and personal experience so far is that if I need several EQs in the chain, they have different purpose and thus end up being different tools ...

QC  is a good eq , I also use others , It is a great eq to be included as a stock eq.
I would us the QC more if we could adjust the the Q with the scroll
wheel on the mouse . yes a pet peeve but work flow is huge :)

twelvetone
...and whilst we're about it, can someone once and for all explain what the Gloss button does? In normal, technically understandable terms?
 
I can't hear any difference.

You should have been able to hear a difference if you used noise for testing (as described in my Friday's Tip of the Week referenced earlier). The fact that you can't is concerning, because it implies a problem with your hearing in the 8 - 20 kHz range.
 
Here's a screen shot of white noise without and with Gloss. Gloss adds a subtle high-frequency lift that starts around 5 kHz, and becomes most prominent in the 8 to 20 kHz range.
 

>>  Gloss adds a subtle high-frequency lift that starts around 5 kHz, and becomes most prominent in the 8 to 20 kHz range.
 
On my Sonar I see a boost of about 1 to 1.5dB.
There must be more to it than that, and it is an explanation of that, in technical terms, that I am trying to discover.

twelvetone
>>  Gloss adds a subtle high-frequency lift that starts around 5 kHz, and becomes most prominent in the 8 to 20 kHz range.
 
On my Sonar I see a boost of about 1 to 1.5dB.
There must be more to it than that, and it is an explanation of that, in technical terms, that I am trying to discover.

It really is as simple as it seems: a subtle "lift" in the highest audible octave to add what people call "air." You could use a shelving EQ to do that, but then you'd have to give up a stage.

Been saying it on here since it was first introduced; Users should be allowed multiple instances of the Quad Curve EQ in a single Pro Channel.  All ProChannel modules should allow this most basic functionality.

EQ , Tube and Compressor seems to be the PC effects that can be only used once. All others you may have multiple instances of. The logic behind it is bizarre.