I am a traveling consultant and I have one. While the response time is not as fast a true wi-fi or DSL connection, I have been able to dial in to my client's VPN (albeit at an agonizingly slow rate) and get some work done. I primarily use it while I am at my client to monitor my company's e-mail (I use a client PC for my day-to-day work).
I actually find it to be very reliable. I wouldn't use it as a primary means of connecting to the internet, but if you need it when out and about, it will do the job. Of course signal stength is key (just like any cell phone).
Regarding location, I live in SE MA, and have used th card in Miami FL and Omaha, NE with no problems.