State of the X-Window
I just watched a presentation on X.org's history, architectural overview, and recent developments, entitled State of the X-Window. If you use an operating system that runs X, I recommend you check it out.
The thing that I found most personally relevant is that there is currently a bug which prevents framebuffer re-allocation. As a result, the framebuffer size is fixed until the X-server is restarted!
This has always been a pain for me, since I can hotplug my external monitor into my laptop flawlessly, but can't switch out of clone to dual head without restarting X (since that would require a framebuffer size increase). The server developer promises that it'll be fixed in the next few months — I'll certainly be excited to have that working!