There, I said it.
It doesn't mean they're totally USELESS; no. For the majority of situations, they're more trouble than they're worth.
First, you have to be in exactly the right situation - there cannot be background noise or crosstalk - so essentially, a nearly SILENT room. How many of us spend a substantial amount of time in silence? I'm certainly not going to use a voice app on a bus, plane, or in public even if it was quiet, because anyone who does that is an obnoxious asshole.
Second, you have to know exactly the syntax the system is looking for. On my stupid car (BMX x5) it has voice activation but I'll be damned if I can ever remember what phrases it wants. "CALL HOME" (doesn't work, oh yeah, have to kick it to the phone menu) "PHONE" phone connected "CALL HOME" many results pick one.
Sigh. Oh, and my wife's name is Dawn, so fuck me if I don't have to sort through every damn "DON" in my phone book, distracting me away from the road while I do that - what am I *saving* using a voice app, again?
Third, you have to inevitably put up with a substantial failure rate. If I try to use a voice app for the simplest thing, dictating a slowly, clearly spoken text, I have to expect to spend the next few moments re-reading, editing, and correcting the text. If I'm trying to use it to come up with harder info - like names, in the example above - it's just a crapton easier to dial the number myself.
And I'm a Minnesotan (a region reputed to have a relatively clear style of speaking). I can't imagine how hard it must be for people with less intellgible accents.