Talking while driving still not safe?

A study by Harvard and the University of Warwick researched the safety of driving while talking and found that people engaged in conversation drove much more poorly than other conditions.

"The worst results came from the subjects tasked with listening to a list of words and then speaking new words that began with the same letters as each word on the list. Those "drivers" had a 480 millisecond delay, which at 60 miles per hour would mean 42.3 additional feet traveled before applying the brakes." 

This task is similar to using an in-vehicle system for command and control purposes.  The driver is speaking to the system and then waiting for it's response and possibly speaking again. A mitigating factor is that typically, speech offers the ability for shortcuts to activate functionality more quickly, reducing the time that drivers are interacting with the system.

In-vehicle systems are not totally hands-free however; they usually are "push to talk" like a Nextel phone or walkie talkies. The driver is end pointing their speech, making the system's job easier.

In-vehicle speech recognition is worth watching, and it may be safer than alternatives, but it still hasn't been shown to actually be safe.