"1. What application you switched from and which version of SONAR you switched to."
I switched from Cubase (LE v3 I think) to Sonar Home Studio after trialing the demo version (of producer).
When upgrading my copy of Sonar later on, I was sent the Producer version by mistake. When I telephoned Cakewalk sales to discuss the error, I was told never mind and was given a key for Producer - result!
"2. Your specific reasons for switching to SONAR (specific features in SONAR, specific problems with other aps, customer service, etc.)"
Steinberg have been chuffing me off with very buggy software since Cubase v2 for the Atari FM platform. They consistently charge for bug fixes (AKA 'upgrades') and then release apparently untested code containing either the same bugs, or more bugs. I finally had enough of paying them money to do this so decided to change. To be honest, I would have definitely considered Logic but it's only supported on the Mac now and I'm not a big fan of that platform. Besides, the cost of changing both computer platform and sequencer software is prohibitive! I'm not sure if my Creamware Pulsar cards would be supported on the Mac either (and I loves 'em).
FWIW, the main differences I've noticed between Cubase and Sonar are very clear-cut.
Sonar simply sounds and grooves much better than Cubase, and the included plugins (synths, effects etc.) are of a far better quality and there are a greater variety of them
Cubase's strength is in the UI. The workflow and tools available (e.g. built-in audio editor and logical editor; please, please include a logic editor in Sonar!!) are better than those in Sonar. Doubtless some of that opinion is due to familiarity, but it's the little things which seems to make more sense in Cubase. For example, record a MIDI clip punching in at 3:1:0 in Cubase, and the clip starts there. In Sonar, it's whenever the first note is played. Being able to create a blank clip to work in. Glueing notes / clips together. Automation handling (resolution, drawing tools). I could go on...
Neither's perfect, but I'm really glad I made the change to Sonar. I can work around the issues in the Sonar UI, but there's no way of making Cubase sound and groove better.