I just did the following, intending to copy the contents of the ../other directory to the current directory:
$ cp ../other/*
Notice the missing . at the end of the command? In my case, there were exactly two files in the other directory. This command doesn't do anything like what you might expect it to do. Instead, it copies the contents of ../other/file1 over the top of the contents of ../other/file2 (because the shell expands the wildcard before cp sees it), destroying file2 in the process. Gah!
As it happens, I luckily had the original file2 open in an editor session so I simply saved it again. The irony of this situation was that I was preparing to add those files to a new Subversion repository so I wouldn't accidentally lose them.