I've had it for about two hours now. Initial impressions: 3D effect is not gimmicky and does not become less noticeable as the time you spend with a game wears on. I've yet to be given a head ache. Face Raiders is hilarious. Pilot Wings (the only game I purchased) is pretty "meh" so far. No data manager yet? No internet browser yet? Disappointing :( Digging the new stylus. AR Cards are incredible, looking forward to seeing more in the future. Mii QR codes seem to hold a lot of redundant data.
Regarding a hacking "scene": Nothing too interesting yet. But if you're a dev you may find it worthwhile to pop into #3dsdev on EFNET.