That file: /etc/.pwd.lock seem to be there on all the machines here with me -> FC2, RH all the way down to RH7.2. - Zero size file owned by root. I found it on a Solaris machine (SunOS-5.6) too! However DEC-OSF1 machines dont have it.
On my FC2 machine, the date of creation of the file matches the installation date. I did a google search for that. Found a similar thread in debian list (its there on debian machines too!), but they too were left clueless.
Wonder what that file does. Its very interesting though. I'll post the question on other lists and get back to this thread if I find any answers.