I was in Las Vegas a few days ago and got to experience Mobile WiMax for the first time via the Sprint/Clearwire network that's been installed there.
My reaction. Think the best of WiFi and a MiFi all rolled into one.
Speeds were solid and I was able to make VoIP and Skype calls, including video, without any problem while seated inside my hotel's restaurant and from a moving car.
Couple of hiccups. First there is a lag time from when you first seek to connect that lasts up to a minute, after that, you'd think you were on a T1 or better as everything just flies. My sending of email via my Exchange server was rocket fast, but I did see some delays on the loading of web pages, so it appears there may be some proxying of port 80 traffic being done by Clearwire or Sprint, but I didn't test for that.
Regardless, with Clearwire/Sprint 4G in Las Vegas at my disposal, it will be one more wireless way to work and stay connected. As more new devices roll out, the uptake will also be greater. This new Overdrive from Sierra Wireless should help there.
You can try out WiMax in Las Vegas via Cheetah Wireless' rental program.
(Note: To be transparent, I'm a minor stakeholder in Cheetah Wireless)