It is common knowledge that ssh -X or ssh -Y forward X11 connections. However, what I didn't know until few days ago is that this works even across several machines. That is, if you do ssh -Y from A -> B -> C, then opening an X program on machine C will forward the X connection to the X server at machine A. Very convenient.
This is interesting: Microsoft gives out the NT kernel source for academic, non-profit use. Too bad I don't have much time to play with it a bit; I've always been impressed by the very NT kernel (which is itself VMS-ish). More details here. A related project is ProjectOZ, a platform (simulator) for teaching principles of operating systems.
After being a long-time user of the fvwm2 window manager, I have switched to Ion. The author, incidentally, dislikes the current state of open-source software, linux (calling it the Idiot-box Linux), and gnome. I share many of his opinions and have subscribed to his blog. Very interesting read!