Hi ,
personally I think it's great.

Updates have usually been nothing more than bug fixes in most of the keyboards I've had to date.

Apart from fixing the odd bug , korg have actually added new sounds , new features & revised some styles in their various upgrades to date.
So personally I'm not complaining, maybe they'll add more new features, sounds etc over the coming months/years. Who knows.

Had a couple of updates for my psr1500, certainly didn't get any new sounds or features, maybe the T2 owners did better?

Ketron SD1+ 4.0c update, haven't got a clue what it was supposed to do, though I did notice some of my midi functions finally worked the way they were supposed to.

I'm finding it more than playable just as it is, (there again I'm only a home keyboardist) No doubt over the coming weeks I'll be delving into the amazing style/pad/ sound editing/creation functions this keyboard has to offer.

Soundwise it leaves my Psr1500 sounding pretty poor, there again not a fair comparison considering the price difference.
As for the SD1+, can't say, the SD1 's upstairs hooked up to a $1,500 sound system, I'm playing the PA800 thru it's own speakers other end of the house.

best wishes
Rikki