Well, I won't really label him as "Homer Simpson" moron (meaning, no matter what he attempts to do, he's still a big moron), I can't say he's completely learned from his mistakes. I mean, as some people on here have said, he still makes newbie mistakes from time to time (even in Hoenn, where they actually played him up to be a mentor.). I mean, sure, he's gotten about... 32 gym badges, a trophy, two Top 16s (BTW, that's COUNTING the Whirl Cup as a League), 7 frontier symbols, two Top 8s, half a ribbon, and some others, but then again, even IF he becomes a Pokemon Champion, that doesn't mean he'll be the World's Best Pokemon Master anytime soon (especially since Bulbapedia hinted that it's not even one of the requirements.).
Actually, that reminds me, they never really bothered to define a "Pokemon Master" in the Anime, which, in one sense, makes his goal more vague than even Misty's Goal of being the worlds greatest Water Pokemon Master (I mean, at least she mentions that what makes a great trainer and master is training water Pokemon for battles, and being very skilled at it, Ash's goal doesn't even begin to define the requirements, thus making it extremely vague.).
Also, speaking of Morons, I'm a bit surprised that Ash and his group seems to be much more susceptible to Team Rocket's disguises now than back in season 1. I mean, at least in Season 1, he and the gang sounded suspicious and unsure about the disguised team rocket. Now, they are easily fooled by even the most pathetically disguised incarnations of Team Rocket (even you, Jorah, have to admit that the quality of the disguises, as well as the groups overall intelligence, is growing smaller by the minute.).
@SBaby, yeah, good point about the cast changes. I mean, most people are still upset at Misty leaving the cast, quite a good deal of them, not to mention, for example. I mean, even IF they had to do cast changes, that doesn't mean they should act as though they never existed at all. Though, I don't necessarily agree with the whole "rotting away" part in regards to Oaks Lab. I mean, it was stated when Oak's Corral was first explored that the pokemon do excercise and the like, and thus, by natural implication, that means they train as well.