Quick tip for easily updating all of your RAW files 'without adjustments' to process 2012. (assuming if like me, you don't automatically just want to update all your files without seeing the effect on those you have worked on - on an as needs basis)
Create a Smart Collection with the following criteria:
1. RAW Files Only
2. Has No adjustments
Lightroom has a default smart collection 'Has No adjustments' however, if you use this it will still include processed Tiffs and other file types such as jpegs and update those as well to the new process 2012 (which you may not want to do without seeing the result - best done image by image as required).
From the new smart collection you create; Take the first image into 'Develop' and select 'Update all Film Strip Photos'. That will update all your RAW files without adjustments to process 2012 ready to work on them in the new pipe.
Worth noting to: Old files may still be using old ACR 3.3 or 4.4 Profiles as well and not the current 'Adobe Standard' (I don't think there is a way to select all ACR 3.3 or 4.4 files as a smart collection to enable updating all to Adobe Standard with one click? If there is, you would probably want to ensure you also use the above two smart collection criteria)
