In short: so I was right on a few fronts: The US Nintendo 3DS will cost $249.99, come with a few built in games, an upgradable 2MB SD card and will get around 30 games within the launch window (March-June). The 3DS has three cameras, can auto-generate a pic of you into a Mii (nice) and will be able to play DS games (not in 3D) as well as downloadable GameBoy and GBA games. Street Pass" is an optional "social networking" function that allows for trading high scores and other data with nearby 3DS units.
3DS will be stores February 26 in Japan, March 27 in the US, March 25 in Europe and UK (which have a quirky "per retailer" price point structure that so far ranges from 219-249 Euros/Pounds - yikes!). The fine folks at engadget have a lot more clout than lil' ol Mii, so here's link to their deeper coverage. I'll have a list of confirmed titles shortly.