Just ran several tests on EDGe and 3G with my iPhone 3G. Overall the speeds from EDGE were as expected … slow. The average speed after 5 tests on 3 different speed test sites using EDGE was 111kbps. The average speed on 3G after 5 tests on 3 different sites was 390kbps. That’s a pretty substantial improvement. I have heard that you can expect about 2.5x from EDGE to 3G. My small sample set shows more than 3.5x improvement.
Again, its a sample test of EDGE to 3G and there are other factors here, like my specific location of my test, others on the network, and so on. Also, i believe that y area just went live on 3G a few days ago, just after the iPhone 3G launch. This may mean that very few people even know 3G is here. Who knows for sure.