2009/8/20 Nguyễn Thái Ngọc Duy [off-list ref]:

grep: turn on --cached for files that is marked skip-worktree
ls-files: do not check for deleted file that is marked skip-worktree
update-index: ignore update request if it's skip-worktree, while still allows removing
diff*: skip worktree version

I kept reminding myself and still managed to miss it. skip-worktree
bit is not completely independent from assume-unchanged. It shares
CE_MATCH_IGNORE_VALID flag in ie_match_stat(). Should have mentioned
that in commit log.
-- 
Duy