I dunno if that has been confirmed or whatever, but the new ad pamphlet that comes in the new DS English/Japanese/Kanji dictionary (that came out yesterday) shows a screenshot of what's either a SMB3-style overworld or a Mario Party board.  I'm guessing the former.  Cool to see yet another element from the old styles coming back, though I did much prefer the SMW overworld to the SMB3/Yoshi's Island one.  It felt a lot more like a real world to me back when I was a kid playing them.

As for the dictionary itself, it seems very good so far.  Certainly better than the one they released last year.  The kanji recognition is brilliant and I've had better luck getting it to figure out what I'm writing than on anything I've ever used before (including a Zaurus).  I'll post more impressions once I've had the time to work with the program more in depth, but I'm definitely not regretting dropping that 4800 yen on it. 

Plus, registering it early snags me this cool case for both cartridges (though the original sort of feels rendered useless by the new software):

http://club.nintendo.jp/cmp/rakubiki/index.html

It was mentioned in Nintendo Power, apparently:
http://www.gamesarefun.com/news.php?newsid=6139

Did Super Mario Bros. 3 actually have multiple exits? I seem to remember that some of the Fortresses did, but I'm pretty sure the normal levels didn't. I do hope the secondary exits in NSMB are real brain-teasers. Some of the ones in Super Mario World had me stumped for months.

Has anyone seen screenshots of the Kooka Kids/Koopalings yet? I miss those little guys, and Koopa, Jr. never really made up for them.

Yep, SMB3's normal levels only had one exit.  Fortresses did too, but there were one or two of them (Worlds 7 and 8) that had multiple doorways which served to throw the player off.

I'm all for secondary exits, but I would much prefer the straightforward nature of a SMB3/Yoshi Island overworld map.  One thing I didn't like about Super Mario World was how one had to keep trekking around that map, with Mario's slow-butt self.  The Star Roads made it somewhat more tolerable, but.....

Actually, my biggest concern is how the game itself will play.  Folks who tried it out at GDC have reported that the mechanics - particularly the jumping - are more akin to the original SMB than SMB3 and SMW, as was originally planned.  Although I'll likely warm up to it in time, it's hard to imagine playing a new Mario game with those stiff-by-today's-standards brand of controls.

Well, there are secret exits in both castles and normal levels leading to bonus rooms, but no exits which are needed to beb able to walk another road on the map. Unlike in Mario World those are accessible right on the map (or by means of the warp flute) and not through different exits from within levels.

Also I reject the impression that the world maps of SMB3 and Yoshi's Island are similar, it's only the graphical presentation that's somewhat similar. While YI is completely linear, SMB3 has plenty branching points where you can freely choose the next level (and feel free to completely skip others).

I suppose you're right there.  Although for myself, the branch-offs are a bit of a moot point, since I end up playing through each and every level anyway. 

In truth, I wouldn't mind a SMB world map either, so long as getting from point to point is a quicker affair.

I liked SMB's original meachanics, because Mario could stop on a near dime and moved briskly.  In SMB3, Mario moved sluggishly.  It took a bit for Mario to get moving and he had more momentum, so stopping on a dime was impossible.  Maybe that was intentional, but it took me some readjustment to play SMB3 and Mario 64-like games.

With that said, though, I did just take a look at some of the gameplay videos from GDC, and...... it's still hard to nail just how Mario will control.  He looks fluent enough, but the nuances of movement and jumping is something one would have to experience first-hand, I suppose.