This. I use Google Voice all the time and give that number out to people who I'm selling something to, 3rd party companies if I need to be reached and so forth. I find it really convenient having 2 numbers going to my phone for instances like Craigslist selling, surveys from sporting events and people I meet that I may not want to keep in contact with for very long.
I do have a separate phone number that keeps my 212 area code for school / job applications and work related stuff. I find it easier to get jobs and get ahold of someone in a big city if you have the area code they're calling from. I keep that number in my Nexus 4 which is rarely used anymore.