Good CONSTRUCTIVE points gentlemen. Unfortunately, both my work and personal numbers are pretty well established. I think it all comes down to if you can start out with a Google voice number it makes the whole process easier. I am not going to change all of my marketing, website, business cards, etc. to make use of GV. I just do not think the benefits outweigh the costs, time and frustration.
You can port an existing number to google voice if you want. You could take your established mobile number and make it your GV number while giving your cell a new "secret" number.
Another feature I forgot to mention (since I have not used it myself in a year or so) is dirt cheap international calling. Rates are about the same as skype but the call can be routed directly to any phone you want instead of stuck on your computer.