I used PDAnet on my Droid back in February because I was travelling and it was the only internet I had for a week. I found that it worked pretty good for most things (facebook including games, this site, macrumors, spike, etc.) Video took a while to buffer but I even watched some TV shows on Hulu.
I don't know how well the mobile broadband works, but you are paying for unlimited internet on your smartphone anyways so why not use it?