Samsung's big Galaxy S 4 update hit Europe a month ago; it's now spreading to the US through Sprint. The American patch adds much of what we saw in its international counterpart, including the option of moving supporting apps to the SD card. Business-minded customers also reportedly get access to the Knox security suite. Just be careful about upgrading if you're planning to install a custom ROM -- XDA-Developers members report that the bootloader has changed, but they haven't yet verified whether or not it's locked down. Those who aren't concerned about flexible firmware should receive the update soon, though, and we're hoping that other US carriers aren't far behind.
Update: Early adopters jumped the gun -- Samsung tells us that this doesn't include Knox. Activation of that service is still coming at a "later date."