I picked up a 46EX400 as a replacement for my old 47" westy that died. I was going to get the EX500, but I didn't get as much store credit as I thought I would, and after staring at the 400 and 500 side by side, there wasn't enough difference for me to justify the extra money. I was fortunately able to get the EX400 for less than the amount of credit I got, so I could also replace (or at least help replace) my PS3.
Anyway, I'm really liking it. I haven't missed the 120hz at all so far, even while watching some March Madness today. The black levels are incredible compared to my old set, so no complaints there. No, they don't quite match some of the Samsungs I saw, but I couldn't tell the difference (side by side comparison at BB and Sony Style) between the 400 and 500.
I haven't quite found the color settings/white balance that I love yet, but the colors are by no means BAD, and again, they are far superior to what I had before with the westy.
It is a VA panel if that matters to you - the 500 probably is as well (though I didn't test it, didn't want to be pushing on the screen in store hehe). I'm not seeing any clouding, the backlight is very even. The only slight niggle here is that one corner appears to be a BIT darker than the rest - not much, but a bit. It isn't that noticeable most of the time.
Sound isn't fantastic, but it isn't horrible for in TV speakers either.
Works well for gaming. I'm not noticing any huge input lag or anything using Game Mode.
Overall, I'm very satisfied. Then again, I personally don't like 120hz/240hz for anything other than sports or animated films. I'm a big fan of the feel of film, and 120hz/240hz just takes that away IMO. If you're looking at the two sets side by side and don't notice a difference in store, I can't think of a reason to take the 500 over the 400. I think it will mainly come down to whether you feel like you need 120hz over 60hz.