I just got the Wi-Fi version this week. The main selling point for the 3G from what I can gather is the ability to get books in a Wi-Fi-less location. I have Wi-Fi at home so I didn't see myself buying many books while on the run. I decided to use the $50 difference on books. I may regret my choice later, but from playing around with the Kindle this week, I'm pretty happy with my choice.
I really like the text to speech function. I can also download my audiobooks from Audible.com to it. You can also download MP3s to play, which I found really cool!
My Kindle has browsing abilities also. But it is super slow. Just good for checking latest news and weather, etc...but hardly something to use as a real browser.