I read this article...
 
http://www.benvesco.com/blog/mixing/2008/turn-a-mono-track-into-rich-stereo/
 
which is about using tiny bits of delay on one channel of a track (or on an identical copy of a mono track) to give a wider sense of space. I played around with it, copying a mono track into a second track and then adding delay to track 2, panning the two tracks all the way to opposite extremes. (If you're an uber-noob like me, it's a fun little experiment to set this up and play with all the variables. You can really hear what is happening.) 
 
No question, right yet. Just thought some other sonar virgin might enjoy it.

It's one of the ways to simulate stereo, there are others.   Here's an article with more info.

 
The Hass effect is also of interest in the design of music rooms.  The same idea, only you play with the room instead of playing with the signal.
 
Who needs a Haas Kicker? is a thread that gives an idea of the fun you can have.
 
 

Tlawhon: thanks, that's a great article. 
 
Paul P: Holy crap! that shiz is deep! Fascinating. 

The "Haas effect" must be separated from the "Haas Trick".
 
I love the sound o the "Haas Trick" on rhythm guitar parts, but I am always mindful of mono-compatibility.
 
 

jb101
The "Haas effect" must be separated from the "Haas Trick".
... I am always mindful of mono-compatibility.
 

I hear you. Somebody tried to pull a Haas trick on me in New Orleans back in the late '70s. Didn't even occur to me to worry about mono, I was so sure I'd gotten the clap. 
 
Wait a sec, I think I'm confused. What's the difference between the effect and the trick?

A couple of questions from the above reading:
 
They talk about mid/side vs Left/Right separation. Does Sonar do Mid/Side processing, or just L/R?
 
Also, the MStereoSpread info said that it only works on a stereo track; in tracking instruments that I expect I'll want to widen (guitar, voice and such), should I make a habit of recording them to stereo tracks even though they are mono sources?
 

ward s
They talk about mid/side vs Left/Right separation. Does Sonar do Mid/Side processing, or just L/R?

Here's an SOS article by Craig Anderton on the subject using Sonar's Channel Tools plugin.
 

However, the signal that arrives first will take precedence and "weight" the image toward that side...which is why this is sometimes called the "precedence effect."

I had a great time playing with it. In the end I got free Haas after the novelty wore off. I think all new to Sonar should spend some time playing with it manually to learn about space
 
P.S. 10ms to about 90ms from both sides till you start hearing the doubling kick in. Then you've gone too far. Pretty cool