Up through Lion, the contents of a Finder window would automatically update when the files within it were changed. This seems to no longer be the case with ML. As an example, I have my Time Machine backup disk mounted. If I open up the /Volumes/Backup/Backups.backupdb/<Computer Name> folder, I see all the backups. If I let Time Machine run, I won't see the newest backup appear unless I close the window and re-open it.
This seems to be new behavior with 10.8. I'm hoping there's a preference I forgot to check or something.