Notes from the PDF iPod Touch Features Guide:
p. 7 — The screenshot from iTunes shows system version 1.1 for the iPod Touch. Presumably version 1.0 was the version of mobile OS X that shipped with the iPhones.
p. 10 — The sleep/wake button is on the top left. On the iPhone, it’s top right. Wonder why they moved it? Also worth noting that on the iPod Touch, the headphone jack is on the bottom.
p. 13 — You can double-click the Home button to bring up on-screen playback controls, even when the screen is locked. Nifty. But, unlike the iPhone, the Touch has no hardware volume buttons, and it doesn’t have a play/pause/next-track clicker on the headphone cable. That clicker is my very favorite thing about the iPhone’s music player; I think it’ll be a pain to use an iPod Touch that’s in your pocket. (AppleInsider notes that you can’t just plug iPhone headphones into an iPod Touch, either — the Touch doesn’t support the clicker.)
p. 16 — iPod Touch supports several keyboard layouts: QWERTY, QWERTZ, AZERTY, QZERTY, and Japanese IME.
p. 17 — Double-tap the space bar while typing to enter a period followed by a space. That shortcut isn’t available (yet?) on the iPhone.
p. 50 — You really can’t add events in the Calendar app on the iPod Touch. Lame.
p. 52 — You can, however, add and edit address book entries in the Contacts app.
p. 63 — Support for closed captioning. The iPhone doesn’t (yet?) have this.
p. 65 — Optional Debug Console for MobileSafari. The iPhone doesn’t (yet?) have this.