I second "writing a thumbdrive from scratch"! There's much more to it than it sounds like. Travis talks for example about the possiblity of the drive being able to fingerprint the system it's mounted on, recognizing it's 'home' machine. From there he suggest counter measures like recognizing an indexing process by the read patterns and have the drive erase itself, or giving a different checksum every time the content is hashed.
You might also find eldoc-mode[1] and it's various mode-specific children (c-, perl-, ...) to a useful minor-mode. It displays a short string describing the function-at-point, and the order and name of it's arguments. Sort of zero-click docs. Whatever way it does it could probably be hacked up to display more complete docs in a split window or frame. Something I'll think about when I finally get an SSD :)
The simplest way is to use netstat and check amount of connections from each host. If you see plenty hosts with many connections established, that's DDoS. If there is plenty hosts, but each one has few connections, thats DoS (aka slash dot effect), mentioned by Tomek_.
PS: DDoS - distributed denial-of-service attack. Deliberate attack which involves dedicated software; DoS - denial-of-service. Server can't handle all requests, because suddenly there is more of them (because of link on frontpage etc)
Sometimes it's not acceptable to store data on external server without root on it.
For these kind of uses Unison (mentioned in previous comments) is decent solution, but also AeroFS (aerofs.com), which works much smoother (less collision problems).
Anyway syncing data on several devices must became standard soon.
