Absolutely love handhelds. I play them all the time while commuting to work (don't worry; I pause when changing trains and look where I'm going; I'm not one of those people), will occasionally fire it up during a break at work, and even at home when the better half is monopolizing the TV.
I'm lucky enough to be able to read Japanese, though, so all those untranslated games are just a minor annoyance rather than a total loss. You'd think that in this age of digital distribution, low-budget translation with the game being sold on the PSN would be a cheap alternative way to get these games out to speakers of other languages, but that's not what we're seeing.
The 3DS has even gone a step further and region-locked their portable, handheld device!
Getting rid of this hassle would go a long way in making handhelds more popular. Let us use them when we travel!
(The pie-in-the-sky solution is the complete elimination of separate markets for separate locales and of the "localization" concept entirely, with games being released in various languages all on the same worldwide network. Games would either have multiple languages to select from on the same disk/ROM, or you would filter for your languages when browsing the PSN.)
One thing I'd like to see, though, is better handheld-to-TV graphic output. The device for the PSP puts out slightly imperfect, under-scaled graphics with colors that are a bit too saturated. There's no reason why this couldn't be better: even emulators can handle this the right way. And the Vita has no graphics out?