[Nottingham] Diagnosing a slow network

[Jason Irwin]

I'm running an rsync from my desktop (Ubuntu 10.10) to a server (Ubuntu
12.04) as a paranoid back-up before upgrading the desktop.

The desktop and server are both SATA units (desktop is RAID0, server is
RAID1), they are connected to the same gigabit switch by CAT6 cables.
There's nothing else really running, so why is rsync showing speed of
only 14MB/s or so?
Surely I should be seeing 100MB/s or something?  (I'm assuming rsync is
displaying mega-bytes and not mega-bits)
How do I set about determining where the bottleneck is?

Or has my total inability to understand anything network-y reared its
head again?

-- 
Jason Irwin