I guess I should have been more specific in the title...I was more interested in which NEW X3 features people were using a lot of not using. But, this is still interesting because it's giving me some ideas for articles about the lesser-used features. Although some people probably aren't using particular features because they truly they don't fit into the style of music they do or their workflow, perhaps some aren't being used because users aren't aware of all the things those features can do.
 
 

Good Points, Craig.  For me, I'm only recording Traditional Country (e.g. I'm currently recording a "retired" Nashville songwriter).  I use an Alesis SR-16 drum machine for the majority of recordings (I did a vocal project for the drummer in our band and even used the Alesis SR-16 for his project).  Vocals, add pedal steel guitar, lead guitar (clean, no distortion), bass and rhythm guitar and that's about it.  I've got repeat customers coming back for more projects so for my clients my formula works.

Well, define new?  as in only in X3?  i can't remember what is brand new since x1 & x2... old age.  Heven't been doing a lot of new songs lately, but love and use most every project:
AD 2 - build/edit midi tracks in it and drop them in X3
Pro channel
console emulation
still use V-Vocal
Comping
loop construction - altho I would like to see an improved version to make it easier to split and shift pitch.  Maybe like you said about a good article on loop construction, altho I've seen a couple.  I still remember how easy Acid Pro was to just split the loop and + or - to shift pitch.... and it seemed to know the best algorithm to use to make it sound good up to may 5-6 semitones off... how easy is that?
eq flyout for fine tuning, but usually just use pro-c
multidock, piano roll, Z3TA+
blue tubes fx - i have and use so many fx i can't keep it straight what came from where.
 
haven't used much at all:
audio snap
melodyne
matrix
gobbler
bus colors - i just use track folders
strum - had it for many years and did a couple of songs with it, but not lately.
TH2 - i have many Amplitube amps
 
 

This should be a useful thread. As an exclusive Producer user my everyday activity makes good use of;
 
1. QuadCurve EQ (tremendous improvement and highly useful, especially in conjunction with Melda MultiAnalyzer (thx BitFlipper)
2. New comping implementation (only looping I ever do is multiple takes ...)
3. Melodyne ARA integration (great example of efficient functional integration, hope to see more examples of this approach)
+ 
Tone2 Bifilter2 (intriguing, one extra I need more time to play with it )
 
Not so useful
1. AD (longtime BFD user and not likely to change especially since BFD3. I did try AD, seems OK if not as deep as BFD)
2. Strum Acoustic Session (prefer real guitars)
3. Lounge Lizard (just not relevant, but I'm sure someone appreciates it.)
 
There are many extras and long time users have complained about yet another amp sim, but for a new user, the overall package is quite comprehensive and a tremendous value.
 
I think it's worthwhile to reinforce a couple of key points for the X series in general. 
1. UI
- Skylight may not be the best name, but given my background in the -science- of visualization, human interaction and  software design, I greatly appreciate the commitment to a major overhaul. Took some guts on the part of CW product mgrs, but absolutely worth the risk. Regarding the many complaints from some long time users, the insight is there are more than one type of users and the more "technical/engineering" types (my apologies in advance for general stereotyping) might have a preferences for the more "detailed" look & feel of say... 8.5. However, I generally see Sonar as a promising tool for the "creative" types (not that engineers are NOT creative, because they are) and the improved workflow and interactivity are greatly enhanced with the new approach. I find it to be a standout compared to the alternatives in my musical community.
2. Multidock/screensets 
- A subset of the UI improvements. Could there be improvements? Maybe, but quite useful as is. 
3. Stability
- This should be first actually. Cannot say enough about the accumulated confidence of daily use on several instances running Win 8.1 64x. But arent they all supposed to be rock solid? I marvel at the fact that it runs on a PC platform which is an infinite mess of variable conditions. Worst case scenario and yet we find utility undreamed at a mere decade or so ago ....
 

For me it's the Quad Curve EQ followed by Melodyne ARA Integration (I have Editor Version).  If I could include pre- X3 features it would definitely be ProChannel at the top with the Console Emulators right behind.

My favorite X3 feature.

Most used would be Comping, Melodyne ARA, QuadCurve EQ flyout, Track Colours and Lounge Lizard (love it).
 
Also love some of the Nomad Plugs (Particularly Pulteq one).
 
I have explored most of the new features, I think, but the least used would be BitFilter, Strum Acoustic,  Gobbler and AD Drums (used to be big Toontrack fan, but AM now exploring other options..)

Using:

• Comping (because I don't get a choice)
• Automation Lanes! (Yes yes a thousand times yes but please fix the paste bugs)
• Color customization (not ideal in my opinion but pretty good once I get used to bright wave/dark clip)
• FX Region with V-Vocal (it's new in X3 and works better than X2 so I'm counting it)
• XLN Addictive Drums (but you can't count this because I was already a full license paid-up user)

Not using:

• Melodyne (because V-Vocal FOR EVER!!!)
• Blue Tube (seriously... will they even be included in X4?)
• Anything new related to ProChannel (because I don't use it)

...I'm probably forgetting something.

Quad curve would be used more if it had mid/side...that is all it is lacking. I like the idea of the Tape sim. I would love to see Cakewalk expand it's capabilities. Melodyne and AD2 were huge for me. I like to use EZD2 for creating midi and then copy to a AD2 track to compare and choose. Blending the "Rock" kit in EZD2 with the Fairfax is a current favorite.
 

I mentioned Pro Channel earlier, but I should specifically mention the Quadcurve EQ,I had plenty of EQ VSTs but this has made them redundant. Likewise the compressors and concrete limiter have marginalised many of my T-Racks plug-ins.
 
I have not dived too deep into Melodyne yet, even though I have upgraded to editor. I want to do more with it, extracting MIDI from Audio. I see potential for using my Mountain Dulcimer as a midi controller, albeit not in real time and using scat vocals as a way of getting melodies down.