Smart Collections are so under used because we have dumb collections and, well people can be lazy. But problem is, they are proprietary. In the case of moving fro LR 2X to 3beta, all those dumb collections break since you can’t import older catalogs today. But recreating the smart collections was super easy because at least in my case, all were based on metadata. The idea of piling images into folders without regard to the structure and instead relying on a dumb collection, or anything that’s proprietary breaks down if you ever decide to move to another DAM product. Too bad some so called LR “experts” are making a lot about dumb collections instead of smart collections and well structured folders of images because I suspect in the future, they and their minions may get bit by this process.
I rely on Smart Collections for all permanent collection I have and all steps in my work flow. I only use the ordinary collections for temporary grouping images together for specific work.