Until one becomes very familiar with PV 2012, I very strongly recommend not batch-converting images with existing adjustments from older process versions (e.g., 2003, 2010) to 2012. Since the underlying algorithms for the Basic tone controls have changed, and in some cases there are no direct equivalents, this means that image appearance may change significantly in some cases. Any issues that arise will be obvious if you update an individual image. But if you batch-update a group of 100 images, potential problems won't be obvious until you individually review the images.
Now, if you were planning to rework some older images anyways, it's fine to update them to PV 2012.