I used it once, but you have to sync/download the address you entered on the computer or mobile phone to your car. It is just as fast if you just sms the address to your phone and enter it manually to the car. I tried the voice help once too. It was nice, but really not that useful when you have a smartphone with build in GPS to look up addresses.
I used edestination when I first got the car because I thought it was cool. Now 6 months later I never do. Only used the voice assist once. In both cases it is much quicker to just type the address in from my phone.