Outside of a comic book convention, I've still never seen a grown adult (or even an older teenager) with a Vita or 3DS out in public in the US/Canada. And just in the last month I've been to Seattle, Vancouver, Las Vegas, and Los Angeles. 

Smartphones have totally killed that part of the market, Sony/Nintendo need to hope that kids still want handhelds enough, but even that market is under assault by cheap mini-tablets.

Ancedontally too, I had many friends in their 20s who got a PSP near launch when it was the "hot" new thing for 2005 and I knew of others who had a DS especially after the Brain Training craze hit.

But none of them have gone back to buy a Vita or 3DS.

In Japan handhelds reign supreme simply because they've effectively replaced home consoles.

I'm in Rio too and I saw 3 or 4 3DS and 3 or 4 Vitas, not that bad. But I'm not able to count the massive numbers of smartphones that are around. I'm probably seeing 3 or 4 every two minutes...

But that isn't a good measure. It's easy to see me with a smartphone or my tablet, but not so much with my Vita. I play it more at home, since the kind of games we saw in handhelds are similar to console ones, demanding longer play sessions. I don't take the Vita with me always because sometime I know that I will work or study and won't be able to play it. But the tablet and smartphone are always there. Looking this way, adullt people will probably use it more at home. Talking about kids, probably we would see more of them in schools.

Anyway, I predicted 36-45 millions. It would demand higher sales tha we are seeing now and probably won't do better than that. I expect that booth 3DS and Vita suffers from a 50~75% drop of final sales compared to their antecessors because of the higher competition with smartphones and tablets. Home consoles will be fine and probably will have higher sales than the current gen ones.