If you installed a fresh 10.0-BETA 1 you might want to turn off the soft update journaling on UFS filesystem including the root filesystem. I experienced two rather nasty crashes on my test system running under VirtualBox and I didn't get my system stable until I turned off soft update journaling on the root file system and ran a full fsck(8) on the filesystem. This is how to do it:
Boot into single user mode by selecting 2) at the loader menu. Press enter when prompted for the single user shell. Then use these commands and nothing else once you are in the single user shell:
Replace ada0p2 with the partition with the root filesystem on your system if it is different than the one used here.
If you have to run fsck(8) on the root filesystem do it in single user mode when the filesystem is mounted read-only.
Boot into single user mode by selecting 2) at the loader menu. Press enter when prompted for the single user shell. Then use these commands and nothing else once you are in the single user shell:
tunefs -j disable /dev/ada0p2
reboot
Replace ada0p2 with the partition with the root filesystem on your system if it is different than the one used here.
If you have to run fsck(8) on the root filesystem do it in single user mode when the filesystem is mounted read-only.