Agreed, Voice Command should be integrated in more apps. Curious that Live Search has its own built-in voice recognition rather than taking advantage of Voice Command if it is installed on device. Wonder how much duplicate code I have on my device because I have both applications.
Related to this, though it's not a native application, it is related. If you haven't see it try jott.com, which is a very useful voice-based application. You basically dial in to the service which does speech to text that you can use to send text messages to yourself or to other people in an address book.
So for example, if I am driving and there is something I want to remind myself I hit the call button on my Bluetooth headset which kicks in Voice Command, I say "Call Jott," which dials the number then Jott says "Who do you want to jott?" I say myself, and it says "Jott yourself <beep> at which point I say what I want to remember and hang up. In a little bit I get a text message with a translation of what I entered, plus an email with a link to the audio recording. Very handy.