For the most part your 7.x-1.x sub-themes will just run on 7.x-2.x, unless it includes Google fonts such as some of the existing commercial themes do. These you should wait for the official 2.x release of those themes before upgrading else you will get a site error when you try to change the theme settings.
Follow these basic steps to properly upgrade from 7.x-1.x to 7.x-2.x. The bare minimum involves just two steps. You will need to judge if you need to do more, but this will get your theme up and running with the new layout engine and responsive layouts.
Last updated 11th November, 2011 - 9:03am