Hmm... my take is, app doesn't progressively become worse but there are just more and more. Similar ideas are implemented over and over (instead of when iPad/iPhone was just out) - nothing is really "cool" any more because of that (more same old). I'd argue the "good" app are as useful as before (how can a pdf mobile reader be less useful today than before?) - but the novelty is no longer there not because of app, the novelty of the tablet+app uniqueness are well exploited (touch-base, mobile, internet connected, GPS..etc.). There won't be a whole lot of "cool app" until there are more novel hardware integrated into a tablet platform.