I'm not that big on voice commands, largely due to social issues. While talking to a person on the other end of a cellphone call is socially acceptable (in certain places), I'm not sure that goes for talking to a computer. Maybe that will seem perfectly normal at some point, for but now you'd probably get some odd looks. And then what happens when someone sitting next to you is speaking commands that are picked up by your computer? They'll have to make it recognize your voice, but what if it's not perfect? What if recordings (a la Sneakers), or even a good impressionist could defeat it? And then there's the issue of sensitive information; nobody is going to spell out personal details and passwords where others can hear. And it's not just out in public. Think about two people in a living room: one is watching TV on the couch, while another is quietly browsing the internet on a PC. How long would the PC user be able to bark out voice commands before the guy trying to watch TV tells her to shut up? But if you live alone and are at home, sure, knock yourself out with voice.
