Wasn't initially too excited about this, but after using it, I like it's inclusion in SONAR. Nice on a touch screen for auditioning, likely won't get a lot of use for actual playing here.
That said, I think it needs a bit of enhancement to make it more useful.
I think this could slip off the page rather quickly (not sure how much use this feature will receive), so please feel free to add your own wishes and feature requests to the thread to maybe give Cake some ideas for the future.
My List:
1) Make it dockable in the Multi-dock
2) Make it resizable
3) Make another screen which shows DRUM PADS (MPC style) instead of Piano Keys. Would be a potentially great tool for integrating with the step sequencer and/or matrix view.

First, thanks for adding the virtual keyboard. What would be helpful for me is a pad controller like Xotopad. Pads that you can assign Midi CCs to that respond to touch or mouse. Xotopad makes it real easy to record expressiveness by for example recording CC11 and CC1 at the same time on an XY axis.

 
Make it resizable.Please. As it is I only get one octave on my Surface Pro screen. Pretty unusable. I rather check patches on the virtual synths keyboard instead. A virtual keyboard is a blessing on a touch screen. But not this size.
 

Would be nice to get velocity control. This can be done as a few iPad apps are doing by initiating velocity depending on what part of the key one strikes. High on the key yield a high velocity and low on the key for lower velocity. Add a velocity curve and preferences/settings for fine adjustments. Perhaps even pitchbend individually on each key. The more features implemented the more usable and useful the virtual keyboard will be. Perhaps even be used to play music. 
 
It would be nice to have a keyboard with similar features and layout as the Linnstrument
http://www.rogerlinndesign.com/linnstrument.html
 
Check this out
http://theappwhisperer.com/2011/02/05/top-10-midi-controller-apps-for-ipad/ 
Any one of these controllers will work just as well on a Windows touchscreen.