About the potential CPU load that you maybe experience - here on the test machines there are absolutely no CPU usage peaks during this operation. VS 2012 is still RC and this might be one of the reasons. The operation is nothing but open of a file and then it is VS that is responsible for the previews.
Regarding the flavored project approach - we started it this way but there are certain limitations which made us to switch to the MPF approach. Also another reason is that we're planning to extend this project in the future - it was only themes, now it is templates and after that who knows. There are pros and cons in both of the approaches and we'll definitely continue to improve Thunder doesn't matter which one we use. We may easily end up with both :)
We really appreciate your feedback and thank you for your suggestions, we'll have them in mind.
All the best,
the Telerik team
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