I haven't tested LTE in Seattle yet, but reviews of LTE phones and adapters find that the 12 Mbps top-end rate AT&T and Verizon cite is often surpassed. The networks have hardly any users, and the two carriers are clearly setting expectations for when the technology takes off—as when millions of 4G-capable iPads leap into use. The larger pool of bandwidth and a better ability to divvy it up, however, will mean that congested LTE networks will remain far more useful than congested 3G networks.
Both AT&T and Verizon Wireless say that their LTE networks will be largely deployed by the end of 2013. Verizon Wireless has made the more explicit statement that it expects its current 3G footprint, reaching more than 95% of the U.S. population, to have LTE by then. AT&T is a bit vaguer about its final goal, although some of its licenses from the FCC have specific targets for population and geographic coverage.
A future-proofed iPad
Apple has future-proofed the latest iPad by adopting 4G. Honestly, I'm a bit surprised that Apple would take the hit in terms of battery, weight, and size in order to put LTE chips in their devices at this early stage of LTE development. But by keeping the price the same as the iPad 2, and improving performance and the display, along with adding support for the fastest 3G flavors and current 4G technology, I don't think anyone will be feeling buyer's remorse.
Of course, LTE lets you download more data faster, and the iPad 2's display means that you can consume images and video at a higher resolution and more frequently. The only unanswered question is how fast you'll burn through data and pay overage fees when you start taking a 4G iPad out into the field.