Okay, so definitely not pocket-sized, then...
With a bigger casing, will they be bringing back the GBA slot? It's also possible for Nintendo to improve the system operating memory, which I hope they'll do, because it's annoying how you get the "out of memory" error when you try to go on some websites.
EDIT: I've just checked the specifications page (it's all in Japanese!)
The DSi LL won't have a GBA slot, but it comes with Brain Training: Arts, Brain Training: Science, and Dictionary free.
Here's what I managed to translate:
Screen Size:4.2 inches
LCD Screen:TFT with 260000 colors
Size:Width 161.0mm
Length 91.4mm
Thickness 21.4mm
Stylus 96.0mm
Pen 129.3mm
Weight:Approx. 314g
Recharge Time:3 hours
Playing Time:13-17 hours (lowest brightness setting)
11-14 hours (low brightness setting)
09-11 hours (medium brightness setting)
06-08 hours (high brightness setting)
04-05 hours (highest brightness setting)
Software:Nintendo DS software
Nintendo DSi software
DSi Ware
Default Software:Nintendo DSi Browser
Flipnote Studio
Brain Training: Arts
Brain Training: Sciences
Dictionary
Input Slots:DS cartridge slot
SD memory card slot
AC charging socket
Stereo headphone socket
Included in Package:DSi LL console
DSi AC recharging adaptor cable
DSi LL pen
DSi stylus
Quick start guide
Full manual

Notice that though the screens are larger, the buttons are not. I'd say the Nintendo are aiming for older consumers based on the type of default software it comes with, although people of all ages will buy it because of the larger screen. No information about its resolution has been released, so we don't know if it will have clearer images than the DSi or the same quality, but just bigger.
Also, Nintendo hasn't said anything about the camera resolution either.