Features you can expect with Google Voice are listed below (as per the their website)
Why use it GV? Well it's a free local number and I love free stuff. If you have a cell phone and live in an area where you have pretty good coverage then why keep a home phone and pay the extra money? Since my home coverage is pretty good I'm getting rid of my land line and I will save about $1200 dollars per year. With today's economy cutting corners are important to everyone.
Instead of giving out your cell phone number for everything give your Google Voice number. Setup is quick and easy, and this will enable you to route your to calls to any number you choose. Get a copy of your voicemails sent directly to your email. Also get a transcribed copy of what the caller has said if you don't have time to listen to the message. You can also send and receive text messages. GV also offer very low international rates, and mobile access.
As cell phones have really taken off in the last decade I think having a land line is not as important as it use to be. Most people always have their cell phone with them anyway. So why not receive calls through the medium you have most. Google Voice is still in the beta stage, but standby to see how the major players in the telecom industry react if people really take to it. I'm sure they will try to complain to congress how Google is not being fair by offering a free service (except for international calls)
Currently GV is only open to those who where Grand Central users, but if I where you I would sign up and get on the waiting list today. I've liked the features in Grand Central and I do believe Google Voice will take it to the next level.
Google number - One number for all your calls and SMS
Google voicemail - Voicemail as easy as email, with transcripts
Voice features - More cool things you can do with Google Voice