I read recently that someone demonstrated a security attack on a PC via the use of automount and a USB stick.
How vulnerable am I to this attack and what steps are developers doing to be proactive against this sort of thing?
You're not vulnerable to the specific attack, but the approach is very interesting. The vulnerabilities used are already fixed.
I've been chatting with Jon Larimer since I heard about his presentation at Shmoo. The defeat of ASLR takes quite a while (Larimer is brute-forcing it on an NX-emu 32bit system -- a relatively easy target -- and for the demo he disabled ASLR to show it more quickly), and at the time hadn't found a workable way to bypass AppArmor (which he also turned off for the demo), so this speaks pretty well to the proactive defenses in Ubuntu. Using 64bit would have made the attack unfeasible.
Regardless, we took the opportunity to ask the Desktop team to find a way to disable auto-mounting when the screen is locked to avoid this kind of "local but unauthenticated" attack, and have been reviewing improvements to the other thumbnailers (adding ASLR and AppArmor profiles).
I've actually written about it here for people interested in more details.