I work using both screensets and tossing stuff over to the second monitor. This includes my effects in one screenset and my Soft synth GUI's in another, Like the others I also put the console over there/ But what I find is you can have a completly different view for each project. The screenset seem attached to each project. On one with a large track count I have the console view spanning both monitors. 
 
Be aware of one pitfall of dual monitors. You might decide to turn it off for some reason. Then you'll open an application  you last dragged over to the second screen and scratch your head wondering why it won't open? 
It's seems stupid but I keep doing this..so don't turn it off. 
This will also screw you up if you back your projects up and then try and open them on your laptop. You have to run your mouse off screen and blindly grab stuff and drag it back. 

The way you use 2 screens or even 3 or 4 screens is a 100% personal choice. Set it up in a way that most benefits the way you work in Sonar. Try everything and anything and then decide what fits your style...
 
CJ

I found the easiest method is to stretch the TV across both screens and use D to open the dock on the right screen.  If needed you can extend it - when working on lot's o synths or lots of channels in the Console view.
 
Right now I have the same thing on two screens, but one is my touch.  I use D a lot more.
 
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