While setting up OpenBSD on my PowerBook, I ran across a problem with GNOME. My mouse would work fine but the moment I tried to type something, key presses would not register and mouse clicks would no longer work. The caps lock lights still worked and I could ssh to the machine so it was not locked up. Restarting X with Ctrl-Alt-Backspace seemed to be the only way out. The problem was the same if GNOME was started from GDM or from startx. FVWM from startx worked fine, so it wasn't a hardware issue.
After much searching I finally stumbled upon a thread from OpenBSD's misc@ email list that matched my problem:
The next email in the thread mentioned problems with XDM, and I too was also experiencing problems with GDM.
The third email pointed me to the right location for the solution, "the second parapgraph of /usr/X11R6/README" which states:
To use xdm from rc.conf, it is necessary to disable /dev/ttyC0 in/etc/ttys, change the 'status' of /dev/ttyC0 to 'off'.
I remember seeing this when I initially set up X but unfortunately I didn't follow the directions (maybe because I was having the problem from startx as well as GDM). Disabling /dev/ttyC0 and rebooting solved the issue.