Yep I totally forgot this morning, so here you are. If you want to know how to generate 1:1 previews in Lightroom 4 after you’ve imported them or on the fly just do this:
1. Select the images you want to build 100% previews for
2. Library menu –> Previews –> Render 1:1 Previews
3. Go make a cuppa, you maybe here sometime….