I have a Sierra AirCard on the Verizon Express Network. Posting from it now on the Acela between NY and Boston - I even happen to be on the 5 minute stretch at 150 mph.

I get between 40-60kbs, but occasional bursts up to 117kbs at some hotels.

[edited to add:]
Latency runs between 300ms and 500ms. Better than GPRS on T-Mobile, which I have tried but didn't like as much. Of course, there are occasional patches of bad latency and dropped packets. The AirCard appears as a network adapter and seems to have good network drop recovery characteristics. Verizon also uses Venturi accelerator software for compressing images (and text, I think) when browsing. I've found it to be good.

[This message has been edited by lensman (edited 09-02-2003).]