Imagine a lab or office in which everyone used an LED in this way. It might be nice.
We looked around for lights and such (I wanted a traffic light) but they were too pricey so we went low-tech.
See for example the ambient orb which can change colour according to what the Dow is doing, to name one example:
Or the nabaztag, the wifi rabbit, who raises his ears to different triggers, such as, I don't know, a broken link on your website or a customer support email landing in your inbox. Pretty cool.
Turns out you can, though:
I would become a slave of my email.
I'm going to set one of these up to monitor my work email. If someone sends a message to me (which is a small minority of messages I receive), it will light up. Then when I'm in bed and feel like hitting the snooze button, I can glance at the LED and determine whether or not I need to get up and check my email or not.
And I don't know how to build a USB device 'with a couple of logic gates'.
I think I'd just spend the $2.40 and use an AT90USB82 instead. It has USB built in so you don't have to wrestle with software USB. I've done software USB on an Atmel and getting 98% of the way there is easy, but I never really trusted the end result.
On the down side, it doesn't come in a DIP package, but you could use any little breakout carrier card to get to the pins. On the plus side you'd have a couple dozen pins to play with.
See http://www.beyondlogic.org/usbnutshell/usb1.shtml for more info.
The controllers on both ends expect a fairly complex protocol (one which you have virtually zero control over - in software).
Some hubs will allow you to selectively turn power on their ports (most just say they do). You can in theory stick leds there.
Do you guys know of other solutions?
IBM and ASUS seem to use stuff in /proc/acpi/asus|ibm ...
The SD-Card interface in my Laptop exports a LED in /sys/class/led... (but it seems not to be connected to anything).
So there is often one or the other thing installed, but how to control them differs.
The extra experience all those around you will have learning morse code to figure out what it is that you're telling them alone is worth an upvote ;)