I would like to address the title of this thread, before it gets out of hand and is locked. (just kidding)
Sonar Popularity and Shortcomings:
As far as popularity goes: PT got there first, the Pro world is Mac-centric, (as Mr. Anderton pointed out elsewhere) and studios are already heavily invested in PT. But its grip is definitely slipping. I had a few small studio owner friends that looked into Sonar, and liked it, but opted to stay with PT for compatibility with other studios.
Shortcomings? Nothing significant. Sure it's PC only, but that doesn't bother me. I have no desire to lay out more cash for over-priced Mac hardware. The learning curve for Sonar was a little daunting for me at first, but I'm making peace with it.
I started out with Guitar Tracks, and absolutely loved it. I record real acoustic instruments for the most part, but I came to a point where I could see the value of mixing in virtual instrument tracks with my live tracks. If Cakewalk had made a version of GT that supported midi instruments I would have been set for life. And they did. But alas, in GTpro4 audio tracks were limited to 2 discrete simultaneous audio recording inputs. Can't do a drum kit or a band with that limitation. Enter Sonar.
I started with X1. The Skylight interface gave me vertigo. Couldn't wrap my head around it. And a few other things left me scratching my head as well. So I decided to try something else. Enter Acoustica Mixcraft.
This little program is a joy to use, simply because it is so easy to use. Not much learning curve there. I saw someone, (I believe it was on this forum) dismiss it as a toy. Well... toys are fun. It's a forward thinking program from a company that takes its motto "software should be easy to use" seriously. Midi implementation is a breeze, mixcraft had take lanes and FX lanes before Sonar. So it should not be too easily dismissed as a toy. But this is not a Mixcraft commercial. I came back to Cakewalk, and here's why:
The interface. (ha ha! the Skylight interface that gave me fits initially) Mixcraft's interface is far too dark, and the controls on the console view are very tiny and have bad contrast colors. (for my eyes anyway) As primarily an audio guy, with just a splash of midi, I spend a lot of my time in the console view. Sonar's bright appearance, with good visual contrast is a big deal for me. These things matter. Mixcraft's emphasis seems to be on building songs with loops and vsti's, and this is a very minor and sometimes non-existent part of what I do. Sonar has these capabilities in spades when I need them, but they are not constantly in my face as the main focus of the DAW. MC sometimes felt like a looping and midi program to which somebody bolted on audio.
Features: I like that Sonar now has take lanes, comping, and FX lanes. The new control bar is nice. (that's one of the things that I didn't like in X1) I like the fact that I can group faders. MC's only option for this is to send tracks to an alternative output bus. Clunky. Sonar has global and track effects bypass. The ability to copy and drag effects from one channel to another. Handy. These are just a few of my favorites. I'm sure many other DAW's have these capabilities as well, but for me it was a choice between Sonar and Mixcraft. I want to choose a program and get to know it inside out. I realized that had I chosen Mixcraft it would have been for the sake of simplicity only, and I feared I would bump up against it shortcomings eventually. Cubase, Studio One, Reaper, etc.? Nah. If I'm going to have a learning curve I'll have it in Sonar. I'm more accustomed to the Cakewalk way of doing things.
Many things have evolved about the Skylight interface, and that, along with my growing familiarity with it, makes it A-OK with me.
Also, I actually like the new membership business model!