There is nothing special about OSX in this case. Just change this to bs=1024 regardless.
1. bs was already included in the post (FWIW the shorthand is '1M' in Linux, and that's 1048576 :-))
2. I was referring to the use of disk vs rdisk (i.e buffered vs unbuffered/raw, see details[0]), which IIRC is a BSD-ism.
Using rdisk gives a tenfold increase in speed here. Without it you're nowhere near USB2 speeds.
[0]: http://lists.apple.com/archives/filesystem-dev/2012/Feb/msg0...