The transformer does not have an RJ45 jack to plug a network cable into.
You can only access a wireless network with the Transformer. Although you can always connect the transformer via USB to a computer. Which is theoretically capable of doing 480 Mbps. Although you will be limited by the read/write speeds of the memory before you max that out anyway.
That said, I am curious to know what the real world throughput people are seeing on various wifi connections they have with the Transformer.
-Suntan