In one sense, not a whole lot: All the major points of our original review, good and bad, still apply (so read that for the complete rundown).
The S30 really is just a marginally improved rendition. The year-old OS moves with a bit more haste; the touchscreen is more responsive (one of the better resistive touchscreens we've used on a feature phone); and the default browser is a smidge better than even the Instinct's original life-changing 1.1 update (the new zoombar for navigating pages is fast and smooth, but the browser does still runs out of memory loading Giz, for instance). The hardware is a bit smoother and feels more natural in your hand, at the cost of being blander, I think.
Its bid at being more open—developers can have at some of the core Java APIs—will apply to the original Instinct as well, so original owners don't have to feel hosed. Honestly though, I'm not entirely sure how much development that's going to yield. A two-device pseudo-smartphone OS is not a very sexy platform to develop for, really.
But, even though its age is definitely starting to show, its well integrated features and pseudo-smarty OS make it one of the best feature phones you can buy on any carrier, and definitely one of the best phones you can buy on Sprint, period. At least until the Palm Pre shows its pretty face. See if you can snag it for under $130 with contract, though.