I want the 3DS because it's basically a portable N64 with slightly improved graphics. The thumbstick is also a nice thing to add.
It's closer to PS2 than N64. The original DS was akin to the Nintendo 64 while the PSP was like a PlayStation 1.5.
As one of the millions of people with a touch screen phone, having to use a stylus feels as backwards as getting up to change the channel instead of using a remote.
I've just been using my fingernail in games that don't use the touchscreen too often. It's just as responsive as the stylus (where as using the actual finger is sort of 50/50). That said, I do prefer using the stylus in general. I wash my hands quite a bit throughout the day (slightly OCD about it), but fingerprints and smudges are still common on my phone. I also don't like the idea of my finger taking up real estate, especially on such a small screen.
I think I will end up getting one in the future though. It's an investment, to be sure. Let's me play DS, DSi, and 3DS games, and since I bought a GBA SP I'll still have GBC and GBA capability. I'm just waiting for some better 3DS games. Gotta have at least ONE that forces me to buy the thing, and there just isn't one right now.
Edit: I'm also actually very interested in homebrew prospects for it too. A stronger processor means better chances of seeing cool games jury rigged over, like possibly Arena *cough cough*, or maybe some virtual novels. That sort of thing.
Not to mention the 3DS is getting its Virtual Console in May, along with the internet browser. It sounds like they plan on sticking to Game Boy Color releases, but I'm sure GBA will be added eventually.
I'd be careful about homebrew. Nintendo has a killswitch and can brick the system after connecting to the internet, if they detect anything they don't like.