One of the big reasons I'm getting the Incredible when I'm eligible for it is because of the integration with Google Voice. I love having one number that I can give out to anyone. if I don't want people to call me, I can simply forward all calls from person XYZ to VM. It's a beautiful thing. I can set up different voice mail for different people. If my friends/family call they get one voice mail. If my co-workers call, they get something else. If someone I don't know calls they get a 3rd voice mail. I even set mine up so my sister gets a different voice mail from my mom. It's pretty cool.
The other thing I like is that I block my caller ID at work. However, I sometimes call someone where I have to show my caller id. I can call them from my Google Voice number in this case. They get a number, but it's no good to them because if they call it, it's blocked and goes to voice mail.
Of course this says nothing about the main point being that it forwards all calls to all my other numbers. People call one number and they get my home number and cell number all at once.