The second thing that grabbed my attention in the Lightroom 5 Beta is what is being termed Smart Previews (aka Offline Mode). Not that you will see much at all, the only hint they exist will be an empty square rather than a square with a question mark when the photo is actually on an external drive that has been removed. If you do have smart previews set up in this situation you can continued to edit and updated the image and metadata (as if the photo was accessible). then next time you connect the missing drive the updates and metadata changes will be synched back into your catalogue. For those that have big phone collections, stored on external hard drives this is a massive thing, and will make life much easier for a travelling photographer (like myself).
Despite all the excitment in the adobe forums,the smart previews it isn’t a panacea for working with large collections in a collaborative environment or even distribution across a LAN, I’ve had a good play around and I really like the feature BUT it is really best described as just Offline Mode, it is still very much single user, single computer oriented.. The smart previews are stored in a separate smart previews. lrdata file beside your active catalogue, storing smaller version of your originals (not thumbnails) and associated metadata. They also maintain the link back to the original photos. So these previews are not suited to transferring your edit settings and metadata around to other locations (eg moving parts of a library of photos to a another computer or hard drive). What several users have noticed is that working on the smart previews rather than the library of originals on an external drive is a lot faster, and so it should be, its working on smaller files and on the local hard disk.