The good folks at Public Knowledge have released a report (with a fun video, embedded below) appropriately titled, "4G + Data Caps = Magic Beans." These are the fraudulent version of magic beans - don't expect any beanstalks to data clouds.
The 4G offered by major wireless carriers (with the notable exception of Sprint) is a waste of money because it comes with strict data caps. These data caps actively discourage the types of activities that 4G enables. Activities that are made possible by 4G, such as watching movies or uploading video to the internet, are made impossible by the data caps. As a result most users will avoid taking advantage of these new services out of fear of incurring large overage fees. That makes capped 4G little more than a bait and switch, like being sold a handful of magic beans.