I don't know if anybody has written up anything on this yet but I found great uses for google voice. I have an Asterisk PBX and have google voice numbers via Google Talk trunks and it works great for the most part. This allows for fully free calls and can be done anonymously!
Also if you are at a hotel, on the road etc. you can set it to call you when someone calls a certain number or you can go online and put the number into the webpage and it will call you and ring that number for you... So you are getting a free call from an hotel or a payphone etc.
The third and most important use I just found for google voice is scanning. Yo make an random account up on google voice enter a phone number it will ring, go online enter the number you would like to scan 212-555-0000 and it will ring your phone in a second. Once your done you hang up and cahnge the number 212-555-0001. This does too things. It keeps you anonymous because it is giving your google voice number and not the number you are dialing from. It even calls toll free!
One draw back is that it doesn't always work good for numbers that do not have supervision. I find that Gtalk has more of an issue with supervision than if you put your direct number in and have you call it but I am noticing a difference between calling from the PSTN network and google voice. So verify that google voice isn't throwing you off.