Why transfer speed over Fast Ethernet (100mbps I think) is only ~1.5MiB/s

Checking Google, 100mbps (Fast Ethernet, wired) is ~12MiB/s but in reality, transferring a file over the network (home LAN) is only ~1.5MiB/s. Why might that be?

I am on Ubuntu 11.10 transferring to Windows 7 (the other direction, copy, gives a similar speed).

Use a tool like IPerf to really see what your TCP throughput is with a well-optimized TCP app. IPerf will also tell you what your default TCP window size is, which might be telling.

Check to make sure all of your Ethernet cables are properly wired. Many people (and cable testers) check for pinout correctness without checking to make sure the conductors from each pin is twisted together with the conductor from the correct paired pin (Hint: 1&2, 3&6).

It's possibly due to interface errors, so check for that (specifically for speed/duplex).

It could also be that the router/switch/hub doesn't have enough juice, so try a crossover connection just to make sure its not that.