Grandpa and I use VZ 3g exclusively. I can tell you that with good reception and low traffic I see spikes up to 2.5 mbps, with average speeds roughly 1.5 mbps. With poor reception and/or heavy traffic it is not unusual to see 500 Kbps or less. A "typical" decent connection is in the range of 800 kbps to 1.1 mpbs.
800 kbps is good enough to stream SD video from amazon or dishanywhere.com. When you see sustained speed in the 500 kbps range you can expect buffering.
If you don't have a Wilson Trucker antenna, get one and mount it high enough for a clear shot. I have one mounted on a short pole and I can go from 2 bars to 4 bars just be walking it around a bit.