Ok - so after almost two weeks on Studio One - thought I'd list a few of my favorite features so far. Perhaps some of these are in SONAR in some fashion and I just didn't know about it. Some I know are not. Might help with anyone considering the move to S1.

1. Mix Effects - S1 has the ability to insert an effect in a special place for the "entire mix" - and no, I'm not talking about just an insert on the master bus - you can insert a plug in ONCE at the top, and it will effect EVERY channel independently BEFORE it hits its channel strip, and of course, before any summing happens.  So what is it for? The first couple plug ins they have for this are console emulators that are way better than what I've seen with regular bus inserts - because it gets to the sound prior to hitting the mixer at all. This allows it to do things like channel cross talk like the old analog boards and gives a great sound!
2. Insert routing splits - I'm talking within an individual track channel , you can split the signal in half, 3rds, 4th, nths, and put whatever inserts you want on each branch - great for example for parallel compression on a single track w/o having to use buses or count on a mix knob on the plug. You can split signal in half straight up or by frequency or stereo channel. I hear M/S splits are coming. The routing editor is like a flow chart editor where you drag inserts and splits around at will ... cool!
3. Powerful and simple to use Macro editor to create shortcuts to do all kinds of more complex crazy stuff. I've already made several and assigned shortcut keys. Not sure what SONAR has in this way, but I guess I never used it if it does.
4. This is one of my favs - the built in Cue Mix - basically allows me to have 0-latency monitoring controlled from the DAW. What it is actually doing is controlling my Fireface 800 mixer from within S1 so I don't have to open the Fireface software separately and can work with friendlier channel names and all in one place with my main mix.
5. How fast I adapted. I feel like I'm 95% as proficient in S1 as I ever was in SONAR working in it for only a week and a half or so. Done 3-4 tracking projects and several mixes. It's real easy to learn - not that dissimilar from SONAR in many of the basics, and pretty intuitive. Once you kind of find where everything is, learn (or change) the key shortcuts, and get a handle on how it does a couple things - very easy. I find I'm already forgetting how to do things in SONAR the "SONAR way" when i go back to it - again - after less than two weeks.
6. Lastly for now - the user community on their forums is very friendly, responsive, and helpful. They are "all hands on deck" for the SONAR users switching over - and I'm seeing lots of those by the way - even have a special sub-forum for SONAR to S1 users.

Anyway - thought this might interest some of you. Perfect? ... no - missing a few things I liked from SONAR? ... yes. But very good, intuitive, and with its own cool features? ... YES! It has my recommendation.

nice review ken.
thanks

Yes, good review. Don't have any desire to jump yet, but S1 sounds like a good compromise.
Also, S1 has ARA which makes using Melodyne a similar experience in Sonar hopefully.

Been doing a lot with Melodyne Studio 4 in Studio One.
 
It works at LEAST as well as in SONAR - and to me - seems even a little more integrated and smooth. Can't exactly put my finger on why ... but any clip - just select and hit Ctrl-M - and poof - up it pops in Melodyne ready to edit. One thing that is nice is that you can still slip edit  and do fades on clips AFTER they have a Melodyne region/editing on them!

Excellent tips Ken, I have been using it as well but had not yet found the Mix FX. Nice find. The router splits are awesome too, I had already been playing with that one. 
 
I find the transient detection and manipulating multi-track drums to be better as well. Once you get around the terminology. Transients are called "Bend Markers" and they don't "Stretch audio" they "Bend audio"
 
gabo

"

This is one of my favs - the built in Cue Mix - basically allows me to have 0-latency monitoring controlled from the DAW. What it is actually doing is controlling my Fireface 800 mixer from within S1 so I don't have to open the Fireface software separately and can work with friendlier channel names and all in one place with my main mix. "

 
I think I will feel the same in a week or two.
Saw a video on this approach they use for monitoring and it sort of blew my head open :)
Have yet to instigate but it looks really interesting.
 
Thanks for the update!

Ken Matson
Been doing a lot with Melodyne Studio 4 in Studio One.
 
It works at LEAST as well as in SONAR - and to me - seems even a little more integrated and smooth. Can't exactly put my finger on why ... but any clip - just select and hit Ctrl-M - and poof - up it pops in Melodyne ready to edit. One thing that is nice is that you can still slip edit  and do fades on clips AFTER they have a Melodyne region/editing on them!

To my knowledge, ARA was developed via a partnership between PreSonus and Celemony. Cakewalk obviously participated in that effort very early on, but the tightest integration with Melodyne I would expect to be with S1P.