$ dd if=/dev/zero of=/dev/null bs=1M count=1K
    1024+0 records in
    1024+0 records out
    1073741824 bytes (1.1 GB) copied, 0.157131 s, 6.8 GB/s

My favorite file manager, Thunar, reports file sizes in decimal units. Not sure if it's distro-specific, though.

Many other programs, like 'df', have a switch (--si) that turns decimal units on or off.

Of course, aficionados of RFCs will know that "octet" is (or at least was) the preferred term for "byte" in IETF documents as well. I don't think this is because the RFC editor was secretly French, although i'm sure he was thoroughly classy; presumably it's because early RFCs were written in the era when the byte had not quite settled down at eight bits, and needed to be unambiguous.

I suppose I should've said that up until five years ago, nearly everyone was using powers of two for file sizes. And Windows/Mac never used the correct prefixes.

It's a tricky topic and as Raymond correctly points out, giving people a term that they don't understand probably serves little to no good purpose.

    $ df -k /
    Filesystem     1K-blocks     Used Available Use% Mounted on
    /dev/sda3      151798672 47602008 102615608  32% /

    $ df -h /
    Filesystem      Size  Used Avail Use% Mounted on
    /dev/sda3       145G   46G   98G  32% /

    $ df -H /
    Filesystem      Size  Used Avail Use% Mounted on
    /dev/sda3       156G   49G  106G  32% /

$ df --version df (GNU coreutils) 8.22

ls has -h/--si/-k ...

    $ ls -h -l /proc/kcore 
    -r-------- 1 root root 128T Apr  6 19:02 /proc/kcore
    $ ls --si -l /proc/kcore 
    -r-------- 1 root root 141T Apr  6 19:03 /proc/kcore