The Big N announced this a week or so back IIRC. It's a completely new DS with bigger screens, 2 cameras, SD card support, and no GBA slot. Just to name a few new features.
Ya know what? With no GBA slot, all of us Pokemon Diamond/Pear players will be effed if we want to transfer our GBA Pocket Monsters to D/P on the DSi. So don't eBay that Phat or Lite juuuust yet.
ALSO: Wii Storage solution is solved!
There is always the DS to solve that. If I was ever bored and wanted to play GBA game, I would keep my DS Lite for that, and DSi would be used for other things. I would consider the DSi a mobile "Wii Media Player". I wouldn't use it for typical playing, more like for taking pics, communicate, etc...
Economic wise. I say its a waste of money... There is already something that can take digital photos and its called a "digital camera". I doubt that its needed for that sort of thing.
As for the fact of no GBA slots. That is just an foolhardy decision, isn't that why most of Nintendo fans bought it for? Without that, not many of the DS games that require it can be played, because it doesn't have it... That just, ruins it... In my opinion.