Well, I do use Sonar, but the older version 8.5.3, and I use it rather minimally. For actual composing I use Finale (2005b), as I prefer to work in notation... and Sonar's reputation when it comes to notation is deservedly horrible. One of the reasons I have never updated to a more recent version of Sonar is the "orphan" status of any notation features in Sonar. I do use Sonar for its MIDI editing, and for mapping controllers. Mixing is done in MIR Pro (used stand-alone on a 2nd computer), and I finally added the Vienna Suite for needed plugins.
I have learned to work in the hybrid manner of Finale > Sonar, and am comfortable doing so, so there has never been a need to change. If I were starting over, I would look very seriously at Cubase, and if I were to upgrade my DAW software, I would likely go in that direction. I am also curious to see what the new notation development team over at Steinberg (the old Sibelius team) will eventually come up with.
As for computers, my DAW is an old Windows XP machine, and MIR Pro is run on a W7 system.